[llvm] r303213 - [InstSimplify] add folds for constant mask of value shifted by constant
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Tue May 16 14:51:05 PDT 2017
Author: spatel
Date: Tue May 16 16:51:04 2017
New Revision: 303213
URL: http://llvm.org/viewvc/llvm-project?rev=303213&view=rev
Log:
[InstSimplify] add folds for constant mask of value shifted by constant
We would eventually catch these via demanded bits and computing known bits in InstCombine,
but I think it's better to handle the simple cases as soon as possible as a matter of efficiency.
This fold allows further simplifications based on distributed ops transforms. eg:
%a = lshr i8 %x, 7
%b = or i8 %a, 2
%c = and i8 %b, 1
InstSimplify can directly fold this now:
%a = lshr i8 %x, 7
Differential Revision: https://reviews.llvm.org/D33221
Modified:
llvm/trunk/lib/Analysis/InstructionSimplify.cpp
llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll
Modified: llvm/trunk/lib/Analysis/InstructionSimplify.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/InstructionSimplify.cpp?rev=303213&r1=303212&r2=303213&view=diff
==============================================================================
--- llvm/trunk/lib/Analysis/InstructionSimplify.cpp (original)
+++ llvm/trunk/lib/Analysis/InstructionSimplify.cpp Tue May 16 16:51:04 2017
@@ -1752,6 +1752,24 @@ static Value *SimplifyAndInst(Value *Op0
(A == Op0 || B == Op0))
return Op0;
+ // A mask that only clears known zeros of a shifted value is a no-op.
+ Value *X;
+ const APInt *Mask;
+ const APInt *ShAmt;
+ if (match(Op1, m_APInt(Mask))) {
+ // If all bits in the inverted and shifted mask are clear:
+ // and (shl X, ShAmt), Mask --> shl X, ShAmt
+ if (match(Op0, m_Shl(m_Value(X), m_APInt(ShAmt))) &&
+ (~(*Mask)).lshr(*ShAmt).isNullValue())
+ return Op0;
+
+ // If all bits in the inverted and shifted mask are clear:
+ // and (lshr X, ShAmt), Mask --> lshr X, ShAmt
+ if (match(Op0, m_LShr(m_Value(X), m_APInt(ShAmt))) &&
+ (~(*Mask)).shl(*ShAmt).isNullValue())
+ return Op0;
+ }
+
// A & (-A) = A if A is a power of two or zero.
if (match(Op0, m_Neg(m_Specific(Op1))) ||
match(Op1, m_Neg(m_Specific(Op0)))) {
Modified: llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll?rev=303213&r1=303212&r2=303213&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll (original)
+++ llvm/trunk/test/Transforms/InstSimplify/AndOrXor.ll Tue May 16 16:51:04 2017
@@ -738,8 +738,7 @@ define i32 @test54(i32 %a, i32 %b) {
define i8 @lshr_perfect_mask(i8 %x) {
; CHECK-LABEL: @lshr_perfect_mask(
; CHECK-NEXT: [[SH:%.*]] = lshr i8 %x, 5
-; CHECK-NEXT: [[MASK:%.*]] = and i8 [[SH]], 7
-; CHECK-NEXT: ret i8 [[MASK]]
+; CHECK-NEXT: ret i8 [[SH]]
;
%sh = lshr i8 %x, 5
%mask = and i8 %sh, 7 ; 0x07
@@ -749,8 +748,7 @@ define i8 @lshr_perfect_mask(i8 %x) {
define <2 x i8> @lshr_oversized_mask_splat(<2 x i8> %x) {
; CHECK-LABEL: @lshr_oversized_mask_splat(
; CHECK-NEXT: [[SH:%.*]] = lshr <2 x i8> %x, <i8 5, i8 5>
-; CHECK-NEXT: [[MASK:%.*]] = and <2 x i8> [[SH]], <i8 -121, i8 -121>
-; CHECK-NEXT: ret <2 x i8> [[MASK]]
+; CHECK-NEXT: ret <2 x i8> [[SH]]
;
%sh = lshr <2 x i8> %x, <i8 5, i8 5>
%mask = and <2 x i8> %sh, <i8 135, i8 135> ; 0x87
@@ -771,8 +769,7 @@ define i8 @lshr_undersized_mask(i8 %x) {
define <2 x i8> @shl_perfect_mask_splat(<2 x i8> %x) {
; CHECK-LABEL: @shl_perfect_mask_splat(
; CHECK-NEXT: [[SH:%.*]] = shl <2 x i8> %x, <i8 6, i8 6>
-; CHECK-NEXT: [[MASK:%.*]] = and <2 x i8> [[SH]], <i8 -64, i8 -64>
-; CHECK-NEXT: ret <2 x i8> [[MASK]]
+; CHECK-NEXT: ret <2 x i8> [[SH]]
;
%sh = shl <2 x i8> %x, <i8 6, i8 6>
%mask = and <2 x i8> %sh, <i8 192, i8 192> ; 0xC0
@@ -782,8 +779,7 @@ define <2 x i8> @shl_perfect_mask_splat(
define i8 @shl_oversized_mask(i8 %x) {
; CHECK-LABEL: @shl_oversized_mask(
; CHECK-NEXT: [[SH:%.*]] = shl i8 %x, 6
-; CHECK-NEXT: [[MASK:%.*]] = and i8 [[SH]], -61
-; CHECK-NEXT: ret i8 [[MASK]]
+; CHECK-NEXT: ret i8 [[SH]]
;
%sh = shl i8 %x, 6
%mask = and i8 %sh, 195 ; 0xC3
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