[llvm] r314698 - [InstCombine] remove one-use restriction for icmp (shr exact X, C1), C2 --> icmp X, (C2<<C1)

[Sanjay Patel via llvm-commits]

Author: spatel
Date: Mon Oct  2 11:26:44 2017
New Revision: 314698

URL: http://llvm.org/viewvc/llvm-project?rev=314698&view=rev
Log:
[InstCombine] remove one-use restriction for icmp (shr exact X, C1), C2 --> icmp X, (C2<<C1)

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/trunk/test/Transforms/InstCombine/icmp-shr.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=314698&r1=314697&r2=314698&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Mon Oct  2 11:26:44 2017
@@ -2058,15 +2058,15 @@ Instruction *InstCombiner::foldICmpShrCo
           (!IsAShr && C->shl(ShAmtVal).lshr(ShAmtVal) == *C)) &&
          "Expected icmp+shr simplify did not occur.");
 
-  // Check if the bits shifted out are known to be zero. If so, we can compare
-  // against the unshifted value:
+  // If the bits shifted out are known zero, compare the unshifted value:
   //  (X & 4) >> 1 == 2  --> (X & 4) == 4.
   Constant *ShiftedCmpRHS = ConstantInt::get(Shr->getType(), *C << ShAmtVal);
-  if (Shr->hasOneUse()) {
-    if (Shr->isExact())
-      return new ICmpInst(Pred, X, ShiftedCmpRHS);
+  if (Shr->isExact())
+    return new ICmpInst(Pred, X, ShiftedCmpRHS);
 
-    // Otherwise strength reduce the shift into an 'and'.
+  if (Shr->hasOneUse()) {
+    // Canonicalize the shift into an 'and':
+    // icmp eq/ne (shr X, ShAmt), C --> icmp eq/ne (and X, HiMask), (C << ShAmt)
     APInt Val(APInt::getHighBitsSet(TypeBits, TypeBits - ShAmtVal));
     Constant *Mask = ConstantInt::get(Shr->getType(), Val);
     Value *And = Builder.CreateAnd(X, Mask, Shr->getName() + ".mask");

Modified: llvm/trunk/test/Transforms/InstCombine/icmp-shr.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp-shr.ll?rev=314698&r1=314697&r2=314698&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp-shr.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp-shr.ll Mon Oct  2 11:26:44 2017
@@ -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 [[SH]], 1024
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 %x, 131072
 ; CHECK-NEXT:    call void @foo(i32 [[SH]])
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;