[ARM] Allow pointer values in ARMCodeGenPrepare

Add pointers to the list of allowed types, but don't try to promote
them. Also fixed a bug with the promotion of undef values, so a new
value is now created instead of mutating in place. We also now only
promote if there's an instruction in the use-def chains other than
the icmp, sinks and sources.

Differential Revision: https://reviews.llvm.org/D50054

llvm-svn: 339754

4 files changed, 327 insertions, 196 deletions

diff --git a/llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp b/llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp
index d0ff4441371..69ecc337820 100644
--- a/llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp
+++ b/llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp
@@ -127,7 +127,9 @@ static bool isSigned(Value *V) {
 static bool isSupportedType(Value *V) {
   LLVM_DEBUG(dbgs() << "ARM CGP: isSupportedType: " << *V << "\n");
   Type *Ty = V->getType();
-  if (Ty->isVoidTy())
+
+  // Allow voids and pointers, these won't be promoted.
+  if (Ty->isVoidTy() || Ty->isPointerTy())
     return true;
 
   if (auto *Ld = dyn_cast<LoadInst>(V))
@@ -150,6 +152,8 @@ static bool isSupportedType(Value *V) {
 /// Many arguments will have the zeroext attribute too, so those would be free
 /// too.
 static bool isSource(Value *V) {
+  if (!isa<IntegerType>(V->getType()))
+    return false;
   // TODO Allow truncs and zext to be sources.
   if (isa<Argument>(V))
     return true;
@@ -222,8 +226,10 @@ static bool isSafeOverflow(Instruction *I) {
 }
 
 static bool shouldPromote(Value *V) {
-  if (!isa<IntegerType>(V->getType()) || isSink(V))
+  if (!isa<IntegerType>(V->getType()) || isSink(V)) {
+    LLVM_DEBUG(dbgs() << "ARM CGP: Don't need to promote: " << *V << "\n");
     return false;
+  }
 
   if (isSource(V))
     return true;
@@ -369,21 +375,19 @@ void IRPromoter::Mutate(Type *OrigTy,
     if (Leaves.count(V))
       continue;
 
-    if (!isa<Instruction>(V))
-      continue;
-
     auto *I = cast<Instruction>(V);
     if (Roots.count(I))
       continue;
 
-    for (auto &U : I->operands()) {
-      if ((U->getType() == ExtTy) || !isSupportedType(&*U))
+    for (unsigned i = 0, e = I->getNumOperands(); i < e; ++i) {
+      Value *Op = I->getOperand(i);
+      if ((Op->getType() == ExtTy) || !isa<IntegerType>(Op->getType()))
         continue;
 
-      if (auto *Const = dyn_cast<ConstantInt>(&*U))
+      if (auto *Const = dyn_cast<ConstantInt>(Op))
         FixConst(Const, I);
-      else if (isa<UndefValue>(&*U))
-        U->mutateType(ExtTy);
+      else if (isa<UndefValue>(Op))
+        I->setOperand(i, UndefValue::get(ExtTy));
     }
 
     if (shouldPromote(I)) {
@@ -398,9 +402,6 @@ void IRPromoter::Mutate(Type *OrigTy,
     if (Leaves.count(V))
       continue;
 
-    if (!isa<Instruction>(V))
-      continue;
-
     if (!shouldPromote(V) || isPromotedResultSafe(V))
       continue;
 
@@ -424,6 +425,9 @@ void IRPromoter::Mutate(Type *OrigTy,
 
     for (unsigned i = 0; i < I->getNumOperands(); ++i) {
       Value *V = I->getOperand(i);
+      if (!isa<IntegerType>(V->getType()))
+        continue;
+
       if (Promoted.count(V) || NewInsts.count(V)) {
         if (auto *Op = dyn_cast<Instruction>(V)) {
 
@@ -466,7 +470,7 @@ bool ARMCodeGenPrepare::isSupportedValue(Value *V) {
     return true;
 
   // Non-instruction values that we can handle.
-  if (isa<ConstantInt>(V) || isa<Argument>(V))
+  if ((isa<Constant>(V) && !isa<ConstantExpr>(V)) || isa<Argument>(V))
     return isSupportedType(V);
 
   if (isa<PHINode>(V) || isa<SelectInst>(V) || isa<ReturnInst>(V) ||
@@ -558,10 +562,6 @@ bool ARMCodeGenPrepare::TryToPromote(Value *V) {
     if (CurrentVisited.count(V))
       return true;
 
-    // Ignore pointer value that aren't instructions.
-    if (!isa<Instruction>(V) && isa<PointerType>(V->getType()))
-      return true;
-
     if (!isSupportedValue(V) || (shouldPromote(V) && !isLegalToPromote(V))) {
       LLVM_DEBUG(dbgs() << "ARM CGP: Can't handle: " << *V << "\n");
       return false;
@@ -578,6 +578,7 @@ bool ARMCodeGenPrepare::TryToPromote(Value *V) {
     if (CurrentVisited.count(V))
       continue;
 
+    // Ignore non-instructions, other than arguments.
     if (!isa<Instruction>(V) && !isSource(V))
       continue;
 
@@ -620,6 +621,17 @@ bool ARMCodeGenPrepare::TryToPromote(Value *V) {
              for (auto *I : CurrentVisited)
                I->dump();
              );
+  unsigned ToPromote = 0;
+  for (auto *V : CurrentVisited) {
+    if (Leaves.count(V))
+      continue;
+    if (Roots.count(cast<Instruction>(V)))
+      continue;
+    ++ToPromote;
+  }
+
+  if (ToPromote < 2)
+    return false;
 
   Promoter->Mutate(OrigTy, CurrentVisited, Leaves, Roots);
   return true;
diff --git a/llvm/test/CodeGen/ARM/arm-cgp-phis-calls-ret.ll b/llvm/test/CodeGen/ARM/arm-cgp-calls.ll
index b3720c7841d..0cb91d97db7 100644
--- a/llvm/test/CodeGen/ARM/arm-cgp-phis-calls-ret.ll
+++ b/llvm/test/CodeGen/ARM/arm-cgp-calls.ll
@@ -1,148 +1,5 @@
-; RUN: llc -mtriple=thumbv7m -arm-disable-cgp=false %s -o - | FileCheck %s --check-prefix=CHECK-COMMON --check-prefix=CHECK-NODSP
-; RUN: llc -mtriple=thumbv8m.main -arm-disable-cgp=false %s -o - | FileCheck %s --check-prefix=CHECK-COMMON --check-prefix=CHECK-NODSP
-; RUN: llc -mtriple=thumbv8m.main -arm-disable-cgp=false -arm-enable-scalar-dsp=true -mcpu=cortex-m33 %s -o - | FileCheck %s --check-prefix=CHECK-COMMON --check-prefix=CHECK-DSP
-; RUN: llc -mtriple=thumbv7em %s -arm-disable-cgp=false -arm-enable-scalar-dsp=true -arm-enable-scalar-dsp-imms=true -o - | FileCheck %s --check-prefix=CHECK-COMMON --check-prefix=CHECK-DSP-IMM
-
-; Test that ARMCodeGenPrepare can handle:
-; - loops
-; - call operands
-; - call return values
-; - ret instructions
-; We use nuw on the arithmetic instructions to avoid complications.
-
-; Check that the arguments are extended but then nothing else is.
-; This also ensures that the pass can handle loops.
-; CHECK-COMMON-LABEL: phi_feeding_phi_args
-; CHECK-COMMON: uxtb
-; CHECK-COMMON: uxtb
-; CHECK-NOT: uxtb
-define void @phi_feeding_phi_args(i8 %a, i8 %b) {
-entry:
-  %0 = icmp ugt i8 %a, %b
-  br i1 %0, label %preheader, label %empty
-
-empty:
-  br label %preheader
-
-preheader:
-  %1 = phi i8 [ %a, %entry ], [ %b, %empty ]
-  br label %loop
-
-loop:
-  %val = phi i8 [ %1, %preheader ], [ %inc2, %if.end ]
-  %cmp = icmp ult i8 %val, 254
-  br i1 %cmp, label %if.then, label %if.else
-
-if.then:
-  %inc = sub nuw i8 %val, 2
-  br label %if.end
-
-if.else:
-  %inc1 = shl nuw i8 %val, 1
-  br label %if.end
-
-if.end:
-  %inc2 = phi i8 [ %inc, %if.then], [ %inc1, %if.else ]
-  %cmp1 = icmp eq i8 %inc2, 255
-  br i1 %cmp1, label %exit, label %loop
-
-exit:
-  ret void
-}
-
-; Same as above, but as the args are zeroext, we shouldn't see any uxts.
-; CHECK-COMMON-LABEL: phi_feeding_phi_zeroext_args
-; CHECK-COMMON-NOT: uxt
-define void @phi_feeding_phi_zeroext_args(i8 zeroext %a, i8 zeroext %b) {
-entry:
-  %0 = icmp ugt i8 %a, %b
-  br i1 %0, label %preheader, label %empty
-
-empty:
-  br label %preheader
-
-preheader:
-  %1 = phi i8 [ %a, %entry ], [ %b, %empty ]
-  br label %loop
-
-loop:
-  %val = phi i8 [ %1, %preheader ], [ %inc2, %if.end ]
-  %cmp = icmp ult i8 %val, 254
-  br i1 %cmp, label %if.then, label %if.else
-
-if.then:
-  %inc = sub nuw i8 %val, 2
-  br label %if.end
-
-if.else:
-  %inc1 = shl nuw i8 %val, 1
-  br label %if.end
-
-if.end:
-  %inc2 = phi i8 [ %inc, %if.then], [ %inc1, %if.else ]
-  %cmp1 = icmp eq i8 %inc2, 255
-  br i1 %cmp1, label %exit, label %loop
-
-exit:
-  ret void
-}
-
-; Just check that phis also work with i16s.
-; CHECK-COMMON-LABEL: phi_i16:
-; CHECK-COMMON-NOT:   uxt
-define void @phi_i16() {
-entry:
-  br label %loop
-
-loop:
-  %val = phi i16 [ 0, %entry ], [ %inc2, %if.end ]
-  %cmp = icmp ult i16 %val, 128
-  br i1 %cmp, label %if.then, label %if.else
-
-if.then:
-  %inc = add nuw i16 %val, 2
-  br label %if.end
-
-if.else:
-  %inc1 = add nuw i16 %val, 1
-  br label %if.end
-
-if.end:
-  %inc2 = phi i16 [ %inc, %if.then], [ %inc1, %if.else ]
-  %cmp1 = icmp ult i16 %inc2, 253
-  br i1 %cmp1, label %loop, label %exit
-
-exit:
-  ret void
-}
-
-; CHECK-COMMON-LABEL: ret_i8
-; CHECK-COMMON-NOT:   uxt
-define i8 @ret_i8() {
-entry:
-  br label %loop
-
-loop:
-  %val = phi i8 [ 0, %entry ], [ %inc2, %if.end ]
-  %cmp = icmp ult i8 %val, 128
-  br i1 %cmp, label %if.then, label %if.else
-
-if.then:
-  %inc = add nuw i8 %val, 2
-  br label %if.end
-
-if.else:
-  %inc1 = add nuw i8 %val, 1
-  br label %if.end
-
-if.end:
-  %inc2 = phi i8 [ %inc, %if.then], [ %inc1, %if.else ]
-  %cmp1 = icmp ult i8 %inc2, 253
-  br i1 %cmp1, label %exit, label %loop
-
-exit:
-  ret i8 %inc2
-}
+; RUN: llc -mtriple=thumbv8 -arm-disable-cgp=false %s -o - | FileCheck %s
+; RUN: llc -mtriple=armv8 -arm-disable-cgp=false %s -o - | FileCheck %s
 
 ; Check that the pass doesn't try to promote the immediate parameters.
 ; CHECK-COMMON-LABEL: call_with_imms
@@ -232,32 +89,12 @@ entry:
   ret i32 undef
 }
 
-; Transform will bail because of the zext
-; Check that d.sroa.0.0.be is promoted passed directly into the tail call.
-; CHECK-COMMON-LABEL: check_zext_phi_call_arg
-; CHECK-COMMON: uxt
-define i32 @check_zext_phi_call_arg() {
-entry:
-  br label %for.cond
-
-for.cond:                                         ; preds = %for.cond.backedge, %entry
-  %d.sroa.0.0 = phi i16 [ 30, %entry ], [ %d.sroa.0.0.be, %for.cond.backedge ]
-  %tobool = icmp eq i16 %d.sroa.0.0, 0
-  br i1 %tobool, label %for.cond.backedge, label %if.then
-
-for.cond.backedge:                                ; preds = %for.cond, %if.then
-  %d.sroa.0.0.be = phi i16 [ %call, %if.then ], [ 0, %for.cond ]
-  br label %for.cond
-
-if.then:                                          ; preds = %for.cond
-  %d.sroa.0.0.insert.ext = zext i16 %d.sroa.0.0 to i32
-  %call = tail call zeroext i16 bitcast (i16 (...)* @f to i16 (i32)*)(i32 %d.sroa.0.0.insert.ext) #2
-  br label %for.cond.backedge
-}
-
-
 ; The call to safe_lshift_func takes two parameters, but they're the same value just one is zext.
+; The transform won't happen because of the zext.
 ; CHECK-COMMON-LABEL: call_zext_i8_i32
+; CHECK-COMMON-NOT: uxt
+; CHECK-COMMON: cmp
+; CHECK-COMMON: uxtb
 define fastcc i32 @call_zext_i8_i32(i32 %p_45, i8 zeroext %p_46) {
 for.cond8.preheader:
   %call217 = call fastcc zeroext i8 @safe_mul_func_uint8_t_u_u(i8 zeroext undef)
@@ -281,7 +118,7 @@ for.end411:                                       ; preds = %for.cond8.preheader
 @g_893 = hidden local_unnamed_addr global %struct.anon zeroinitializer, align 4
 @g_82 = hidden local_unnamed_addr global i32 0, align 4
 
-; Test that the transform bails on finding a call which returns a i16**
+; Test that the transform bails on finding %conv4, a trunc
 ; CHECK-COMMON-LABEL: call_return_pointer
 ; CHECK-COMMON: sxth
 ; CHECK-COMMON-NOT: uxt
@@ -308,16 +145,40 @@ if.then:                                          ; preds = %for.cond
   br label %for.cond.backedge
 }
 
-declare noalias i16** @func_62(i8 zeroext %p_63, i32 %p_64, i16 signext %p_65, i32* nocapture readnone %p_66)
-declare fastcc signext i16 @safe_sub_func_int16_t_s_s(i16 signext %si2)
-declare dso_local fastcc i64 @safe_sub_func_int64_t_s_s(i64, i64)
-declare dso_local fastcc zeroext i8 @safe_lshift_func(i8 zeroext, i32)
-declare dso_local fastcc zeroext i8 @safe_mul_func_uint8_t_u_u(i8 returned zeroext)
+; Transform will bail because of the zext
+; Check that d.sroa.0.0.be is promoted passed directly into the tail call.
+; CHECK-COMMON-LABEL: check_zext_phi_call_arg
+; CHECK-COMMON: uxt
+; CHECK-COMMON: uxt
+define i32 @check_zext_phi_call_arg() {
+entry:
+  br label %for.cond
 
-declare dso_local i32 @e(...) local_unnamed_addr #1
-declare dso_local zeroext i16 @f(...) local_unnamed_addr #1
+for.cond:                                         ; preds = %for.cond.backedge, %entry
+  %d.sroa.0.0 = phi i16 [ 30, %entry ], [ %d.sroa.0.0.be, %for.cond.backedge ]
+  %tobool = icmp eq i16 %d.sroa.0.0, 0
+  br i1 %tobool, label %for.cond.backedge, label %if.then
+
+for.cond.backedge:                                ; preds = %for.cond, %if.then
+  %d.sroa.0.0.be = phi i16 [ %call, %if.then ], [ 0, %for.cond ]
+  br label %for.cond
 
+if.then:                                          ; preds = %for.cond
+  %d.sroa.0.0.insert.ext = zext i16 %d.sroa.0.0 to i32
+  %call = tail call zeroext i16 bitcast (i16 (...)* @f to i16 (i32)*)(i32 %d.sroa.0.0.insert.ext) #2
+  br label %for.cond.backedge
+}
+
+declare i32 @assert(...)
 declare i8 @dummy_i8(i8)
 declare i8 @dummy2(i8*, i8, i8)
 declare i16 @dummy3(i16)
-declare i32 @assert(...)
+
+declare dso_local i32 @e(...) local_unnamed_addr #1
+declare dso_local zeroext i16 @f(...) local_unnamed_addr #1
+
+declare noalias i16** @func_62(i8 zeroext %p_63, i32 %p_64, i16 signext %p_65, i32* nocapture readnone %p_66)
+declare fastcc signext i16 @safe_sub_func_int16_t_s_s(i16 signext %si2)
+declare dso_local fastcc i64 @safe_sub_func_int64_t_s_s(i64, i64)
+declare dso_local fastcc zeroext i8 @safe_lshift_func(i8 zeroext, i32)
+declare dso_local fastcc zeroext i8 @safe_mul_func_uint8_t_u_u(i8 returned zeroext)
diff --git a/llvm/test/CodeGen/ARM/arm-cgp-phis-ret.ll b/llvm/test/CodeGen/ARM/arm-cgp-phis-ret.ll
new file mode 100644
index 00000000000..65588b84f7c
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/arm-cgp-phis-ret.ll
@@ -0,0 +1,174 @@
+; RUN: llc -mtriple=thumbv7m -arm-disable-cgp=false %s -o - | FileCheck %s --check-prefix=CHECK-COMMON --check-prefix=CHECK-NODSP
+; RUN: llc -mtriple=thumbv8m.main -arm-disable-cgp=false %s -o - | FileCheck %s --check-prefix=CHECK-COMMON --check-prefix=CHECK-NODSP
+; RUN: llc -mtriple=thumbv8m.main -arm-disable-cgp=false -arm-enable-scalar-dsp=true -mcpu=cortex-m33 %s -o - | FileCheck %s --check-prefix=CHECK-COMMON --check-prefix=CHECK-DSP
+; RUN: llc -mtriple=thumbv7em %s -arm-disable-cgp=false -arm-enable-scalar-dsp=true -arm-enable-scalar-dsp-imms=true -o - | FileCheck %s --check-prefix=CHECK-COMMON --check-prefix=CHECK-DSP-IMM
+
+; Test that ARMCodeGenPrepare can handle:
+; - loops
+; - call operands
+; - call return values
+; - ret instructions
+; We use nuw on the arithmetic instructions to avoid complications.
+
+; Check that the arguments are extended but then nothing else is.
+; This also ensures that the pass can handle loops.
+; CHECK-COMMON-LABEL: phi_feeding_phi_args
+; CHECK-COMMON: uxtb
+; CHECK-COMMON: uxtb
+; CHECK-NOT: uxtb
+define void @phi_feeding_phi_args(i8 %a, i8 %b) {
+entry:
+  %0 = icmp ugt i8 %a, %b
+  br i1 %0, label %preheader, label %empty
+
+empty:
+  br label %preheader
+
+preheader:
+  %1 = phi i8 [ %a, %entry ], [ %b, %empty ]
+  br label %loop
+
+loop:
+  %val = phi i8 [ %1, %preheader ], [ %inc2, %if.end ]
+  %cmp = icmp ult i8 %val, 254
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %inc = sub nuw i8 %val, 2
+  br label %if.end
+
+if.else:
+  %inc1 = shl nuw i8 %val, 1
+  br label %if.end
+
+if.end:
+  %inc2 = phi i8 [ %inc, %if.then], [ %inc1, %if.else ]
+  %cmp1 = icmp eq i8 %inc2, 255
+  br i1 %cmp1, label %exit, label %loop
+
+exit:
+  ret void
+}
+
+; Same as above, but as the args are zeroext, we shouldn't see any uxts.
+; CHECK-COMMON-LABEL: phi_feeding_phi_zeroext_args
+; CHECK-COMMON-NOT: uxt
+define void @phi_feeding_phi_zeroext_args(i8 zeroext %a, i8 zeroext %b) {
+entry:
+  %0 = icmp ugt i8 %a, %b
+  br i1 %0, label %preheader, label %empty
+
+empty:
+  br label %preheader
+
+preheader:
+  %1 = phi i8 [ %a, %entry ], [ %b, %empty ]
+  br label %loop
+
+loop:
+  %val = phi i8 [ %1, %preheader ], [ %inc2, %if.end ]
+  %cmp = icmp ult i8 %val, 254
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %inc = sub nuw i8 %val, 2
+  br label %if.end
+
+if.else:
+  %inc1 = shl nuw i8 %val, 1
+  br label %if.end
+
+if.end:
+  %inc2 = phi i8 [ %inc, %if.then], [ %inc1, %if.else ]
+  %cmp1 = icmp eq i8 %inc2, 255
+  br i1 %cmp1, label %exit, label %loop
+
+exit:
+  ret void
+}
+
+; Just check that phis also work with i16s.
+; CHECK-COMMON-LABEL: phi_i16:
+; CHECK-COMMON-NOT:   uxt
+define void @phi_i16() {
+entry:
+  br label %loop
+
+loop:
+  %val = phi i16 [ 0, %entry ], [ %inc2, %if.end ]
+  %cmp = icmp ult i16 %val, 128
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %inc = add nuw i16 %val, 2
+  br label %if.end
+
+if.else:
+  %inc1 = add nuw i16 %val, 1
+  br label %if.end
+
+if.end:
+  %inc2 = phi i16 [ %inc, %if.then], [ %inc1, %if.else ]
+  %cmp1 = icmp ult i16 %inc2, 253
+  br i1 %cmp1, label %loop, label %exit
+
+exit:
+  ret void
+}
+
+; CHECK-COMMON-LABEL: ret_i8
+; CHECK-COMMON-NOT:   uxt
+define i8 @ret_i8() {
+entry:
+  br label %loop
+
+loop:
+  %val = phi i8 [ 0, %entry ], [ %inc2, %if.end ]
+  %cmp = icmp ult i8 %val, 128
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %inc = add nuw i8 %val, 2
+  br label %if.end
+
+if.else:
+  %inc1 = add nuw i8 %val, 1
+  br label %if.end
+
+if.end:
+  %inc2 = phi i8 [ %inc, %if.then], [ %inc1, %if.else ]
+  %cmp1 = icmp ult i8 %inc2, 253
+  br i1 %cmp1, label %exit, label %loop
+
+exit:
+  ret i8 %inc2
+}
+
+; CHECK-COMMON-LABEL: phi_multiple_undefs
+; CHECK-COMMON-NOT:   uxt
+define i16 @phi_multiple_undefs(i16 zeroext %arg) {
+entry:
+  br label %loop
+
+loop:
+  %val = phi i16 [ undef, %entry ], [ %inc2, %if.end ]
+  %cmp = icmp ult i16 %val, 128
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %inc = add nuw i16 %val, 2
+  br label %if.end
+
+if.else:
+  %inc1 = add nuw i16 %val, 1
+  br label %if.end
+
+if.end:
+  %inc2 = phi i16 [ %inc, %if.then], [ %inc1, %if.else ]
+  %unrelated = phi i16 [ undef, %if.then ], [ %arg, %if.else ]
+  %cmp1 = icmp ult i16 %inc2, 253
+  br i1 %cmp1, label %loop, label %exit
+
+exit:
+  ret i16 %unrelated
+}
diff --git a/llvm/test/CodeGen/ARM/arm-cgp-pointers.ll b/llvm/test/CodeGen/ARM/arm-cgp-pointers.ll
new file mode 100644
index 00000000000..3d396f33ce9
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/arm-cgp-pointers.ll
@@ -0,0 +1,84 @@
+; RUN: llc -mtriple=thumbv8 -arm-disable-cgp=false %s -o - | FileCheck %s
+; RUN: llc -mtriple=armv8 -arm-disable-cgp=false %s -o - | FileCheck %s
+
+; CHECK-LABEL: phi_pointers
+; CHECK-NOT: uxt
+define void @phi_pointers(i16* %a, i16* %b, i8 zeroext %M, i8 zeroext %N) {
+entry:
+  %add = add nuw i8 %M, 1
+  %and = and i8 %add, 1
+  %cmp = icmp ugt i8 %add, %N
+  %base = select i1 %cmp, i16* %a, i16* %b
+  %other = select i1 %cmp, i16* %b, i16* %b
+  br label %loop
+
+loop:
+  %ptr = phi i16* [ %base, %entry ], [ %gep, %loop ]
+  %idx = phi i8 [ %and, %entry ], [ %inc, %loop ]
+  %load = load i16, i16* %ptr, align 2
+  %inc = add nuw nsw i8 %idx, 1
+  %gep = getelementptr inbounds i16, i16* %ptr, i8 %inc
+  %cond = icmp eq i16* %gep, %other
+  br i1 %cond, label %exit, label %loop
+
+exit:
+  ret void
+}
+
+; CHECK-LABEL: phi_pointers_null
+; CHECK-NOT: uxt
+define void @phi_pointers_null(i16* %a, i16* %b, i8 zeroext %M, i8 zeroext %N) {
+entry:
+  %add = add nuw i8 %M, 1
+  %and = and i8 %add, 1
+  %cmp = icmp ugt i8 %add, %N
+  %base = select i1 %cmp, i16* %a, i16* %b
+  %other = select i1 %cmp, i16* %b, i16* %b
+  %cmp.1 = icmp eq i16* %base, %other
+  br i1 %cmp.1, label %fail, label %loop
+
+fail:
+  br label %loop
+
+loop:
+  %ptr = phi i16* [ %base, %entry ], [ null, %fail ], [ %gep, %if.then ]
+  %idx = phi i8 [ %and, %entry ], [ 0, %fail ], [ %inc, %if.then ]
+  %undef = icmp eq i16* %ptr, undef
+  br i1 %undef, label %exit, label %if.then
+
+if.then:
+  %load = load i16, i16* %ptr, align 2
+  %inc = add nuw nsw i8 %idx, 1
+  %gep = getelementptr inbounds i16, i16* %ptr, i8 %inc
+  %cond = icmp eq i16* %gep, %other
+  br i1 %cond, label %exit, label %loop
+
+exit:
+  ret void
+}
+
+declare i8 @do_something_with_ptr(i8, i16*)
+
+; CHECK-LABEL: call_pointer
+; CHECK-NOT: uxt
+define i8 @call_pointer(i8 zeroext %x, i8 zeroext %y, i16* %a, i16* %b) {
+  %or = or i8 %x, %y
+  %shr = lshr i8 %or, 1
+  %add = add nuw i8 %shr, 2
+  %cmp = icmp ne i8 %add, 0
+  %ptr = select i1 %cmp, i16* %a, i16* %b
+  %call = tail call zeroext i8 @do_something_with_ptr(i8 %shr, i16* %ptr)
+  ret i8 %call
+}
+
+; CHECK-LABEL: pointer_to_pointer
+; CHECK-NOT: uxt
+define i16 @pointer_to_pointer(i16** %arg, i16 zeroext %limit) {
+entry:
+  %addr = load i16*, i16** %arg
+  %val = load i16, i16* %addr
+  %add = add nuw i16 %val, 7
+  %cmp = icmp ult i16 %add, 256
+  %res = select i1 %cmp, i16 128, i16 255
+  ret i16 %res
+}