revert r314698 - [InstCombine] remove one-use restriction for icmp (shr exact X,...

There is a bot failure that appears to be related to this change:
http://lab.llvm.org:8011/builders/clang-cmake-armv7-a15-selfhost-neon/builds/2117

...so reverting to confirm that and attempting to keep the bot green while investigating.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@314984 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineCompares.cpp b/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 4b1705ca69c3e83821e7eb1e2234babd4398aa2b..20d8a2785b8ba4d24269961a6f9dbf74b328a560 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -2057,15 +2057,15 @@ Instruction *InstCombiner::foldICmpShrConstant(ICmpInst &Cmp,
           (!IsAShr && C.shl(ShAmtVal).lshr(ShAmtVal) == C)) &&
          "Expected icmp+shr simplify did not occur.");
 
-  // If the bits shifted out are known zero, compare the unshifted value:
+  // Check if the bits shifted out are known to be zero. If so, we can compare
+  // against the unshifted value:
   //  (X & 4) >> 1 == 2  --> (X & 4) == 4.
   Constant *ShiftedCmpRHS = ConstantInt::get(Shr->getType(), C << ShAmtVal);
-  if (Shr->isExact())
-    return new ICmpInst(Pred, X, ShiftedCmpRHS);
-
   if (Shr->hasOneUse()) {
-    // Canonicalize the shift into an 'and':
-    // icmp eq/ne (shr X, ShAmt), C --> icmp eq/ne (and X, HiMask), (C << ShAmt)
+    if (Shr->isExact())
+      return new ICmpInst(Pred, X, ShiftedCmpRHS);
+
+    // Otherwise strength reduce the shift into an 'and'.
     APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal));
     Constant *Mask = ConstantInt::get(Shr->getType(), Val);
     Value *And = Builder.CreateAnd(X, Mask, Shr->getName() + ".mask");

diff --git a/test/Transforms/InstCombine/icmp-shr.ll b/test/Transforms/InstCombine/icmp-shr.ll
index 214f315f31785f4adf772cfed12f6ba627752ec1..77eaf09eb967ce14eed553748309649cc5d3d096 100644 (file)
--- a/test/Transforms/InstCombine/icmp-shr.ll
+++ b/test/Transforms/InstCombine/icmp-shr.ll
@@ -483,7 +483,7 @@ declare void @foo(i32)
 define i1 @exact_multiuse(i32 %x) {
 ; CHECK-LABEL: @exact_multiuse(
 ; CHECK-NEXT:    [[SH:%.*]] = lshr exact i32 %x, 7
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 %x, 131072
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[SH]], 1024
 ; CHECK-NEXT:    call void @foo(i32 [[SH]])
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;