[PATCH] D31120: [InstCombine] Teach SimplifyDemandedUseBits that adding or subtractings 0s from every bit below the highest demanded bit can be simplified
Craig Topper via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Fri Mar 31 14:23:36 PDT 2017
craig.topper updated this revision to Diff 93705.
craig.topper added a comment.
Found another way of testing this particular transform.
https://reviews.llvm.org/D31120
Files:
lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
test/Transforms/InstCombine/and2.ll
Index: test/Transforms/InstCombine/and2.ll
===================================================================
--- test/Transforms/InstCombine/and2.ll
+++ test/Transforms/InstCombine/and2.ll
@@ -126,8 +126,7 @@
define i32 @test11(i32 %a, i32 %b) {
; CHECK-LABEL: @test11(
; CHECK-NEXT: [[X:%.*]] = shl i32 [[A:%.*]], 8
-; CHECK-NEXT: [[Y:%.*]] = add i32 [[X]], [[B:%.*]]
-; CHECK-NEXT: [[Z:%.*]] = and i32 [[Y]], 128
+; CHECK-NEXT: [[Z:%.*]] = and i32 [[B:%.*]], 128
; CHECK-NEXT: [[W:%.*]] = mul i32 [[Z]], [[X]]
; CHECK-NEXT: ret i32 [[W]]
;
@@ -142,8 +141,7 @@
define i32 @test12(i32 %a, i32 %b) {
; CHECK-LABEL: @test12(
; CHECK-NEXT: [[X:%.*]] = shl i32 [[A:%.*]], 8
-; CHECK-NEXT: [[Y:%.*]] = add i32 [[X]], [[B:%.*]]
-; CHECK-NEXT: [[Z:%.*]] = and i32 [[Y]], 128
+; CHECK-NEXT: [[Z:%.*]] = and i32 [[B:%.*]], 128
; CHECK-NEXT: [[W:%.*]] = mul i32 [[Z]], [[X]]
; CHECK-NEXT: ret i32 [[W]]
;
@@ -158,8 +156,7 @@
define i32 @test13(i32 %a, i32 %b) {
; CHECK-LABEL: @test13(
; CHECK-NEXT: [[X:%.*]] = shl i32 [[A:%.*]], 8
-; CHECK-NEXT: [[Y:%.*]] = sub i32 [[B:%.*]], [[X]]
-; CHECK-NEXT: [[Z:%.*]] = and i32 [[Y]], 128
+; CHECK-NEXT: [[Z:%.*]] = and i32 [[B:%.*]], 128
; CHECK-NEXT: [[W:%.*]] = mul i32 [[Z]], [[X]]
; CHECK-NEXT: ret i32 [[W]]
;
Index: lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
===================================================================
--- lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -538,7 +538,7 @@
SimplifyDemandedBits(I, 0, DemandedFromOps, LHSKnownZero, LHSKnownOne,
Depth + 1) ||
ShrinkDemandedConstant(I, 1, DemandedFromOps) ||
- SimplifyDemandedBits(I, 1, DemandedFromOps, LHSKnownZero, LHSKnownOne,
+ SimplifyDemandedBits(I, 1, DemandedFromOps, RHSKnownZero, RHSKnownOne,
Depth + 1)) {
// Disable the nsw and nuw flags here: We can no longer guarantee that
// we won't wrap after simplification. Removing the nsw/nuw flags is
@@ -548,6 +548,15 @@
BinOP.setHasNoUnsignedWrap(false);
return I;
}
+
+ // If we are known to be adding/subtracting zeros to every bit below
+ // the highest demanded bit, we just return the other side.
+ if ((DemandedFromOps & RHSKnownZero) == DemandedFromOps)
+ return I->getOperand(0);
+ // We can't do this with the LHS for subtraction.
+ if (I->getOpcode() == Instruction::Add &&
+ (DemandedFromOps & LHSKnownZero) == DemandedFromOps)
+ return I->getOperand(1);
}
// Otherwise just hand the add/sub off to computeKnownBits to fill in
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