Revert "Revert "[IndVars] Canonicalize comparisons between non-negative values and indvars""

It seems that the patch was reverted by mistake. Clang testing showed failure of the
MathExtras.SaturatingMultiply test, however I was unable to reproduce the issue on the
fresh code base and was able to confirm that the transformation introduced by the change
does not happen in the said test. This gives a strong confidence that the actual reason of
the failure of the initial patch was somewhere else, and that problem now seems to be
fixed. Re-submitting the change to confirm that.

llvm-svn: 307244

5 files changed, 62 insertions, 6 deletions

diff --git a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
index 4ebafd8ea78..29f68ed3060 100644
--- a/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
@@ -264,6 +264,10 @@ void SimplifyIndvar::eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) {
     ICmp->setPredicate(InvariantPredicate);
     ICmp->setOperand(0, NewLHS);
     ICmp->setOperand(1, NewRHS);
+  } else if (ICmpInst::isSigned(Pred) &&
+             SE->isKnownNonNegative(S) && SE->isKnownNonNegative(X)) {
+    DEBUG(dbgs() << "INDVARS: Turn to unsigned comparison: " << *ICmp << '\n');
+    ICmp->setPredicate(ICmpInst::getUnsignedPredicate(Pred));
   } else
     return;
 
diff --git a/llvm/test/Analysis/ScalarEvolution/guards.ll b/llvm/test/Analysis/ScalarEvolution/guards.ll
index 52ad4dc73d4..d4b1f431ffc 100644
--- a/llvm/test/Analysis/ScalarEvolution/guards.ll
+++ b/llvm/test/Analysis/ScalarEvolution/guards.ll
@@ -19,7 +19,7 @@ entry:
 loop:
 ; CHECK: loop:
 ; CHECK:  call void (i1, ...) @llvm.experimental.guard(i1 true) [ "deopt"() ]
-; CHECK:  %iv.inc.cmp = icmp slt i32 %iv.inc, %len
+; CHECK:  %iv.inc.cmp = icmp ult i32 %iv.inc, %len
 ; CHECK:  call void (i1, ...) @llvm.experimental.guard(i1 %iv.inc.cmp) [ "deopt"() ]
 ; CHECK: leave:
 
@@ -41,7 +41,7 @@ leave:
 
 define void @test_2(i32 %n, i32* %len_buf) {
 ; CHECK-LABEL: @test_2(
-; CHECK:  [[LEN_SEXT:%[^ ]+]] = sext i32 %len to i64
+; CHECK:  [[LEN_ZEXT:%[^ ]+]] = zext i32 %len to i64
 ; CHECK:  br label %loop
 
 entry:
@@ -52,7 +52,7 @@ loop:
 ; CHECK: loop:
 ; CHECK:  %indvars.iv = phi i64 [ %indvars.iv.next, %loop ], [ 0, %entry ]
 ; CHECK:  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
-; CHECK:  %iv.inc.cmp = icmp slt i64 %indvars.iv.next, [[LEN_SEXT]]
+; CHECK:  %iv.inc.cmp = icmp ult i64 %indvars.iv.next, [[LEN_ZEXT]]
 ; CHECK:  call void (i1, ...) @llvm.experimental.guard(i1 %iv.inc.cmp) [ "deopt"() ]
 ; CHECK: leave:
 
diff --git a/llvm/test/Transforms/IndVarSimplify/canonicalize-cmp.ll b/llvm/test/Transforms/IndVarSimplify/canonicalize-cmp.ll
new file mode 100644
index 00000000000..93dc968af6a
--- /dev/null
+++ b/llvm/test/Transforms/IndVarSimplify/canonicalize-cmp.ll
@@ -0,0 +1,52 @@
+; RUN: opt -S -indvars < %s | FileCheck %s
+
+; Check that we replace signed comparisons between non-negative values with
+; unsigned comparisons if we can.
+
+target datalayout = "n8:16:32:64"
+
+define i32 @test_01(i32 %a, i32 %b, i32* %p) {
+
+; CHECK-LABEL: @test_01(
+; CHECK-NOT:   icmp slt
+; CHECK:       %cmp1 = icmp ult i32 %iv, 100
+; CHECK:       %cmp2 = icmp ult i32 %iv, 100
+; CHECK-NOT:   %cmp3
+; CHECK:       %exitcond = icmp ne i32 %iv.next, 1000
+
+entry:
+  br label %loop.entry
+
+loop.entry:
+  %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop.be ]
+  %cmp1 = icmp slt i32 %iv, 100
+  br i1 %cmp1, label %b1, label %b2
+
+b1:
+  store i32 %iv, i32* %p
+  br label %merge
+
+b2:
+  store i32 %a, i32* %p
+  br label %merge
+
+merge:
+  %cmp2 = icmp ult i32 %iv, 100
+  br i1 %cmp2, label %b3, label %b4
+
+b3:
+  store i32 %iv, i32* %p
+  br label %loop.be
+
+b4:
+  store i32 %b, i32* %p
+  br label %loop.be
+
+loop.be:
+  %iv.next = add i32 %iv, 1
+  %cmp3 = icmp slt i32 %iv.next, 1000
+  br i1 %cmp3, label %loop.entry, label %exit
+
+exit:
+  ret i32 %iv
+}
diff --git a/llvm/test/Transforms/IndVarSimplify/eliminate-comparison.ll b/llvm/test/Transforms/IndVarSimplify/eliminate-comparison.ll
index 612f01e3cad..a63617e62c0 100644
--- a/llvm/test/Transforms/IndVarSimplify/eliminate-comparison.ll
+++ b/llvm/test/Transforms/IndVarSimplify/eliminate-comparison.ll
@@ -111,7 +111,7 @@ return:
 ; Indvars should not turn the second loop into an infinite one.
 
 ; CHECK-LABEL: @func_11(
-; CHECK: %tmp5 = icmp slt i32 %__key6.0, 10
+; CHECK: %tmp5 = icmp ult i32 %__key6.0, 10
 ; CHECK-NOT: br i1 true, label %noassert68, label %unrolledend
 
 define i32 @func_11() nounwind uwtable {
@@ -163,7 +163,7 @@ declare void @llvm.trap() noreturn nounwind
 
 ; In this case the second loop only has a single iteration, fold the header away
 ; CHECK-LABEL: @func_12(
-; CHECK: %tmp5 = icmp slt i32 %__key6.0, 10
+; CHECK: %tmp5 = icmp ult i32 %__key6.0, 10
 ; CHECK: br i1 true, label %noassert68, label %unrolledend
 define i32 @func_12() nounwind uwtable {
 entry:
diff --git a/llvm/test/Transforms/IndVarSimplify/widen-loop-comp.ll b/llvm/test/Transforms/IndVarSimplify/widen-loop-comp.ll
index b87cd055019..2d24cd732ce 100644
--- a/llvm/test/Transforms/IndVarSimplify/widen-loop-comp.ll
+++ b/llvm/test/Transforms/IndVarSimplify/widen-loop-comp.ll
@@ -64,7 +64,7 @@ for.end:
 ; CHECK-LABEL: @test2
 ; CHECK: for.body4.us
 ; CHECK: %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
-; CHECK: %cmp2.us = icmp slt i64
+; CHECK: %cmp2.us = icmp ult i64
 ; CHECK-NOT: %2 = trunc i64 %indvars.iv.next to i32
 ; CHECK-NOT: %cmp2.us = icmp slt i32