[llvm] r235250 - [InstCombine] (mul nsw 1, INT_MIN) != (shl nsw 1, 31)

[David Majnemer]

Author: majnemer
Date: Fri Apr 17 23:41:30 2015
New Revision: 235250

URL: http://llvm.org/viewvc/llvm-project?rev=235250&view=rev
Log:
[InstCombine] (mul nsw 1, INT_MIN) != (shl nsw 1, 31)

Multiplying INT_MIN by 1 doesn't trigger nsw.  However, shifting 1 into
the sign bit *does* trigger nsw.

Modified:
    llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
    llvm/trunk/test/Transforms/InstCombine/mul.ll

Modified: llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp?rev=235250&r1=235249&r2=235250&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp (original)
+++ llvm/trunk/lib/Transforms/InstCombine/InstCombineMulDivRem.cpp Fri Apr 17 23:41:30 2015
@@ -217,12 +217,16 @@ Instruction *InstCombiner::visitMul(Bina
         NewCst = getLogBase2Vector(CV);
 
       if (NewCst) {
+        unsigned Width = NewCst->getType()->getPrimitiveSizeInBits();
         BinaryOperator *Shl = BinaryOperator::CreateShl(NewOp, NewCst);
 
         if (I.hasNoUnsignedWrap())
           Shl->setHasNoUnsignedWrap();
-        if (I.hasNoSignedWrap() && NewCst->isNotMinSignedValue())
-          Shl->setHasNoSignedWrap();
+        if (I.hasNoSignedWrap()) {
+          uint64_t V;
+          if (match(NewCst, m_ConstantInt(V)) && V != Width - 1)
+            Shl->setHasNoSignedWrap();
+        }
 
         return Shl;
       }

Modified: llvm/trunk/test/Transforms/InstCombine/mul.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/mul.ll?rev=235250&r1=235249&r2=235250&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/mul.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/mul.ll Fri Apr 17 23:41:30 2015
@@ -288,3 +288,19 @@ define i32 @test31(i32 %V) {
 ; CHECK:      %[[mul:.*]] = shl i32 %V, zext (i1 icmp ne (i32* inttoptr (i64 1 to i32*), i32* @PR22087) to i32)
 ; CHECK-NEXT: ret i32 %[[mul]]
 }
+
+define i32 @test32(i32 %X) {
+; CHECK-LABEL: @test32
+  %mul = mul nsw i32 %X, -2147483648
+  ret i32 %mul
+; CHECK:      %[[shl:.*]] = shl i32 %X, 31
+; CHECK-NEXT: ret i32 %[[shl]]
+}
+
+define i32 @test33(i32 %X) {
+; CHECK-LABEL: @test33
+  %mul = mul nsw i32 %X, 1073741824
+; CHECK:      %[[shl:.*]] = shl nsw i32 %X, 30
+; CHECK-NEXT: ret i32 %[[shl]]
+  ret i32 %mul
+}