[ARM] Fix FixConst for ARMCodeGenPrepare

Part of FixConsts wrongly assumes either a 8- or 16-bit constant
which can result in the wrong constants being generated during
promotion.

Differential Revision: https://reviews.llvm.org/D52032

llvm-svn: 342140

2 files changed, 13 insertions, 21 deletions

diff --git a/llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp b/llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp
index bc33e65b067..28bb482a3be 100644
--- a/llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp
+++ b/llvm/lib/Target/ARM/ARMCodeGenPrepare.cpp
@@ -271,13 +271,6 @@ static bool isSafeOverflow(Instruction *I) {
     return true;
   }
 
-  // Otherwise, if an instruction is using a negative immediate we will need
-  // to fix it up during the promotion.
-  for (auto &Op : I->operands()) {
-    if (auto *Const = dyn_cast<ConstantInt>(Op))
-      if (Const->isNegative())
-        return false;
-  }
   return false;
 }
 
@@ -370,19 +363,9 @@ void IRPromoter::Mutate(Type *OrigTy,
   };
 
   auto FixConst = [&](ConstantInt *Const, Instruction *I) {
-    Constant *NewConst = nullptr;
-    if (isSafeOverflow(I)) {
-      NewConst = (Const->isNegative()) ?
-        ConstantExpr::getSExt(Const, ExtTy) :
-        ConstantExpr::getZExt(Const, ExtTy);
-    } else {
-      uint64_t NewVal = *Const->getValue().getRawData();
-      if (Const->getType() == Type::getInt16Ty(Ctx))
-        NewVal &= 0xFFFF;
-      else
-        NewVal &= 0xFF;
-      NewConst = ConstantInt::get(ExtTy, NewVal);
-    }
+    Constant *NewConst = isSafeOverflow(I) && Const->isNegative() ?
+      ConstantExpr::getSExt(Const, ExtTy) :
+      ConstantExpr::getZExt(Const, ExtTy);
     I->replaceUsesOfWith(Const, NewConst);
   };
 
diff --git a/llvm/test/CodeGen/ARM/arm-cgp-icmps.ll b/llvm/test/CodeGen/ARM/arm-cgp-icmps.ll
index a24cdab559f..7ecd3ac6fc4 100644
--- a/llvm/test/CodeGen/ARM/arm-cgp-icmps.ll
+++ b/llvm/test/CodeGen/ARM/arm-cgp-icmps.ll
@@ -1,4 +1,4 @@
-; RUN: llc -mtriple=thumbv8.main -mcpu=cortex-m33 %s -arm-disable-cgp=false -o - | FileCheck %s --check-prefix=CHECK-COMMON --check-prefix=CHECK-NODSP
+; RUN: llc -mtriple=thumbv8m.main -mcpu=cortex-m33 %s -arm-disable-cgp=false -o - | FileCheck %s --check-prefix=CHECK-COMMON --check-prefix=CHECK-NODSP
 ; RUN: llc -mtriple=thumbv7em %s -arm-disable-cgp=false -arm-enable-scalar-dsp=true -o - | FileCheck %s --check-prefix=CHECK-COMMON --check-prefix=CHECK-DSP
 ; RUN: llc -mtriple=thumbv8 %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
 
@@ -279,3 +279,12 @@ entry:
   ret i32 %res
 }
 
+; CHECK-COMMON-LABEL: icmp_i15
+; CHECK-COMMON: movw [[MINUS_ONE:r[0-9]+]], #32767
+define i32 @icmp_i15(i15 zeroext %arg0, i15 zeroext %arg1) {
+  %xor = xor i15 %arg0, -1
+  %cmp = icmp eq i15 %xor, %arg1
+  %res = select i1 %cmp, i32 21, i32 42
+  ret i32 %res
+}
+