From: Craig Topper <craig.topper@gmail.com>
Date: Wed, 22 Mar 2017 04:03:53 +0000 (+0000)
Subject: [InstCombine] Teach SimplifyDemandedUseBits to shrink Constants on the left side... 
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=2612791ba8f92ac0726623bc7df3eef6f59be922;p=llvm

[InstCombine] Teach SimplifyDemandedUseBits to shrink Constants on the left side of subtracts

Summary: Subtracts can have constants on the left side, but we don't shrink them based on demanded bits. This patch fixes that to match the right hand side.

Reviewers: davide, majnemer, spatel, sanjoy, hfinkel

Reviewed By: spatel

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D31119

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@298478 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index b4cc534dd53..41d4a4820bf 100644
--- a/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -533,7 +533,8 @@ Value *InstCombiner::SimplifyDemandedUseBits(Value *V, APInt DemandedMask,
       // Right fill the mask of bits for this ADD/SUB to demand the most
       // significant bit and all those below it.
       APInt DemandedFromOps(APInt::getLowBitsSet(BitWidth, BitWidth-NLZ));
-      if (SimplifyDemandedBits(I->getOperandUse(0), DemandedFromOps,
+      if (ShrinkDemandedConstant(I, 0, DemandedFromOps) ||
+          SimplifyDemandedBits(I->getOperandUse(0), DemandedFromOps,
                                LHSKnownZero, LHSKnownOne, Depth + 1) ||
           ShrinkDemandedConstant(I, 1, DemandedFromOps) ||
           SimplifyDemandedBits(I->getOperandUse(1), DemandedFromOps,
diff --git a/test/Transforms/InstCombine/sub.ll b/test/Transforms/InstCombine/sub.ll
index b756f6a571e..03946c7dbe6 100644
--- a/test/Transforms/InstCombine/sub.ll
+++ b/test/Transforms/InstCombine/sub.ll
@@ -701,3 +701,46 @@ define i8 @bool_sext_sub_nuw(i8 %x, i1 %y) {
   ret i8 %sub
 }
 
+define i32 @test49(i32 %X) {
+; CHECK-LABEL: @test49(
+; CHECK-NEXT:    [[SUB:%.*]] = sub i32 1, [[X:%.*]]
+; CHECK-NEXT:    [[RES:%.*]] = and i32 [[SUB]], 64
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+  %sub = sub i32 129, %X
+  %res = and i32 %sub, 64
+  ret i32 %res
+}
+
+define i32 @test50(i32 %X) {
+; CHECK-LABEL: @test50(
+; CHECK-NEXT:    [[SUB:%.*]] = sub i32 1, [[X:%.*]]
+; CHECK-NEXT:    [[RES:%.*]] = and i32 [[SUB]], 127
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+  %sub = sub i32 129, %X
+  %res = and i32 %sub, 127
+  ret i32 %res
+}
+
+define i32 @test51(i32 %X) {
+; CHECK-LABEL: @test51(
+; CHECK-NEXT:    [[SUB:%.*]] = sub i32 126, [[X:%.*]]
+; CHECK-NEXT:    [[RES:%.*]] = and i32 [[SUB]], 64
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+  %sub = sub i32 254, %X
+  %res = and i32 %sub, 64
+  ret i32 %res
+}
+
+define i32 @test52(i32 %X) {
+; CHECK-LABEL: @test52(
+; CHECK-NEXT:    [[SUB:%.*]] = sub i32 126, [[X:%.*]]
+; CHECK-NEXT:    [[RES:%.*]] = and i32 [[SUB]], 127
+; CHECK-NEXT:    ret i32 [[RES]]
+;
+  %sub = sub i32 254, %X
+  %res = and i32 %sub, 127
+  ret i32 %res
+}