[llvm-commits] [llvm] r126643 - in /llvm/trunk: lib/Transforms/InstCombine/InstCombineCompares.cpp test/Transforms/InstCombine/icmp.ll

[Nick Lewycky]

Author: nicholas
Date: Mon Feb 28 02:31:40 2011
New Revision: 126643

URL: http://llvm.org/viewvc/llvm-project?rev=126643&view=rev
Log:
Teach InstCombine to fold "(shr exact X, Y) == 0" --> X == 0, fixing #1 from
PR9343.

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

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp?rev=126643&r1=126642&r2=126643&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineCompares.cpp Mon Feb 28 02:31:40 2011
@@ -1289,13 +1289,21 @@
   }
     
   case Instruction::LShr:         // (icmp pred (shr X, ShAmt), CI)
-  case Instruction::AShr:
-    // Only handle equality comparisons of shift-by-constant.
-    if (ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1)))
-      if (Instruction *Res = FoldICmpShrCst(ICI, cast<BinaryOperator>(LHSI),
-                                            ShAmt))
+  case Instruction::AShr: {
+    // Handle equality comparisons of shift-by-constant.
+    BinaryOperator *BO = cast<BinaryOperator>(LHSI);
+    if (ConstantInt *ShAmt = dyn_cast<ConstantInt>(LHSI->getOperand(1))) {
+      if (Instruction *Res = FoldICmpShrCst(ICI, BO, ShAmt))
         return Res;
+    }
+
+    // Handle exact shr's.
+    if (ICI.isEquality() && BO->isExact() && BO->hasOneUse()) {
+      if (RHSV.isMinValue())
+        return new ICmpInst(ICI.getPredicate(), BO->getOperand(0), RHS);
+    }
     break;
+  }
     
   case Instruction::SDiv:
   case Instruction::UDiv:

Modified: llvm/trunk/test/Transforms/InstCombine/icmp.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/icmp.ll?rev=126643&r1=126642&r2=126643&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/icmp.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/icmp.ll Mon Feb 28 02:31:40 2011
@@ -387,3 +387,20 @@
   %C = icmp slt i32 %B, 0
   ret i1 %C
 }
+
+; PR9343 #1
+; CHECK: test40
+; CHECK %B = icmp eq i32 %X, 0
+define i1 @test40(i32 %X, i32 %Y) {
+  %A = ashr exact i32 %X, %Y
+  %B = icmp eq i32 %A, 0
+  ret i1 %B
+}
+
+; CHECK: test41
+; CHECK %B = icmp ne i32 %X, 0
+define i1 @test41(i32 %X, i32 %Y) {
+  %A = lshr exact i32 %X, %Y
+  %B = icmp ne i32 %A, 0
+  ret i1 %B
+}