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[InstCombine] try difference-of-shifts factorization before negator 

We need to preserve wrapping flags to allow better folds.
The cases with geps may be non-intuitive, but that appears to agree with Alive2:
https://alive2.llvm.org/ce/z/JQcqw7
We create 'nsw' ops independent from the original wrapping on the sub.
This commit is contained in:
Sanjay Patel 2020-11-24 13:33:12 -05:00
parent ccf6f15bc6
commit 678b9c5dde
3 changed files with 22 additions and 30 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

7
llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
View File

@ -1722,6 +1722,10 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
return Res;
}
// Try this before Negator to preserve NSW flag.
if (Instruction *R = factorizeMathWithShlOps(I, Builder))
return R;
if (Constant *C = dyn_cast<Constant>(Op0)) {
Value *X;
Constant *C2;
@ -1770,9 +1774,6 @@ Instruction *InstCombinerImpl::visitSub(BinaryOperator &I) {
if (Value *V = SimplifyUsingDistributiveLaws(I))
return replaceInstUsesWith(I, V);
if (Instruction *R = factorizeMathWithShlOps(I, Builder))
return R;
if (I.getType()->isIntOrIntVectorTy(1))
return BinaryOperator::CreateXor(Op0, Op1);

15
llvm/test/Transforms/InstCombine/sub-gep.ll
View File

@ -125,9 +125,8 @@ define i64 @test_inbounds2_nuw_swapped([0 x i32]* %base, i64 %idx) {
define i64 @test_inbounds_two_gep([0 x i32]* %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @test_inbounds_two_gep(
; CHECK-NEXT: [[P2_IDX:%.*]] = shl nsw i64 [[IDX2:%.*]], 2
; CHECK-NEXT: [[P1_IDX_NEG:%.*]] = mul i64 [[IDX:%.*]], -4
; CHECK-NEXT: [[GEPDIFF:%.*]] = add i64 [[P1_IDX_NEG]], [[P2_IDX]]
; CHECK-NEXT: [[TMP1:%.*]] = sub nsw i64 [[IDX2:%.*]], [[IDX:%.*]]
; CHECK-NEXT: [[GEPDIFF:%.*]] = shl nsw i64 [[TMP1]], 2
; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%p1 = getelementptr inbounds [0 x i32], [0 x i32]* %base, i64 0, i64 %idx
@ -140,9 +139,8 @@ define i64 @test_inbounds_two_gep([0 x i32]* %base, i64 %idx, i64 %idx2) {
define i64 @test_inbounds_nsw_two_gep([0 x i32]* %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @test_inbounds_nsw_two_gep(
; CHECK-NEXT: [[P2_IDX:%.*]] = shl nsw i64 [[IDX2:%.*]], 2
; CHECK-NEXT: [[P1_IDX_NEG:%.*]] = mul i64 [[IDX:%.*]], -4
; CHECK-NEXT: [[GEPDIFF:%.*]] = add i64 [[P1_IDX_NEG]], [[P2_IDX]]
; CHECK-NEXT: [[TMP1:%.*]] = sub nsw i64 [[IDX2:%.*]], [[IDX:%.*]]
; CHECK-NEXT: [[GEPDIFF:%.*]] = shl nsw i64 [[TMP1]], 2
; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%p1 = getelementptr inbounds [0 x i32], [0 x i32]* %base, i64 0, i64 %idx
@ -155,9 +153,8 @@ define i64 @test_inbounds_nsw_two_gep([0 x i32]* %base, i64 %idx, i64 %idx2) {
define i64 @test_inbounds_nuw_two_gep([0 x i32]* %base, i64 %idx, i64 %idx2) {
; CHECK-LABEL: @test_inbounds_nuw_two_gep(
; CHECK-NEXT: [[P2_IDX:%.*]] = shl nsw i64 [[IDX2:%.*]], 2
; CHECK-NEXT: [[P1_IDX_NEG:%.*]] = mul i64 [[IDX:%.*]], -4
; CHECK-NEXT: [[GEPDIFF:%.*]] = add i64 [[P1_IDX_NEG]], [[P2_IDX]]
; CHECK-NEXT: [[TMP1:%.*]] = sub nsw i64 [[IDX2:%.*]], [[IDX:%.*]]
; CHECK-NEXT: [[GEPDIFF:%.*]] = shl nsw i64 [[TMP1]], 2
; CHECK-NEXT: ret i64 [[GEPDIFF]]
;
%p1 = getelementptr inbounds [0 x i32], [0 x i32]* %base, i64 0, i64 %idx

30
llvm/test/Transforms/InstCombine/sub.ll
View File

@ -1505,9 +1505,8 @@ define <2 x i8> @sub_mask_lowbits_splat_extra_use(<2 x i8> %x, <2 x i8>* %p) {
define i16 @sub_nsw_mul_nsw(i16 %x, i16 %y) {
; CHECK-LABEL: @sub_nsw_mul_nsw(
; CHECK-NEXT: [[X8:%.*]] = shl nsw i16 [[X:%.*]], 3
; CHECK-NEXT: [[Y8_NEG:%.*]] = mul i16 [[Y:%.*]], -8
; CHECK-NEXT: [[R:%.*]] = add i16 [[Y8_NEG]], [[X8]]
; CHECK-NEXT: [[TMP1:%.*]] = sub nsw i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = shl nsw i16 [[TMP1]], 3
; CHECK-NEXT: ret i16 [[R]]
;
%x8 = mul nsw i16 %x, 8
@ -1518,9 +1517,8 @@ define i16 @sub_nsw_mul_nsw(i16 %x, i16 %y) {
define i16 @sub_nuw_mul_nsw(i16 %x, i16 %y) {
; CHECK-LABEL: @sub_nuw_mul_nsw(
; CHECK-NEXT: [[X8:%.*]] = shl nsw i16 [[X:%.*]], 2
; CHECK-NEXT: [[Y8_NEG:%.*]] = mul i16 [[Y:%.*]], -4
; CHECK-NEXT: [[R:%.*]] = add i16 [[Y8_NEG]], [[X8]]
; CHECK-NEXT: [[TMP1:%.*]] = sub i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = shl i16 [[TMP1]], 2
; CHECK-NEXT: ret i16 [[R]]
;
%x8 = mul nsw i16 %x, 4
@ -1531,9 +1529,8 @@ define i16 @sub_nuw_mul_nsw(i16 %x, i16 %y) {
define i16 @sub_mul_nsw(i16 %x, i16 %y) {
; CHECK-LABEL: @sub_mul_nsw(
; CHECK-NEXT: [[X8:%.*]] = shl nsw i16 [[X:%.*]], 4
; CHECK-NEXT: [[Y8_NEG:%.*]] = mul i16 [[Y:%.*]], -16
; CHECK-NEXT: [[R:%.*]] = add i16 [[Y8_NEG]], [[X8]]
; CHECK-NEXT: [[TMP1:%.*]] = sub i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = shl i16 [[TMP1]], 4
; CHECK-NEXT: ret i16 [[R]]
;
%x8 = mul nsw i16 %x, 16
@ -1544,9 +1541,8 @@ define i16 @sub_mul_nsw(i16 %x, i16 %y) {
define i16 @sub_nsw_mul_nuw(i16 %x, i16 %y) {
; CHECK-LABEL: @sub_nsw_mul_nuw(
; CHECK-NEXT: [[X8:%.*]] = shl nuw i16 [[X:%.*]], 3
; CHECK-NEXT: [[Y8_NEG:%.*]] = mul i16 [[Y:%.*]], -8
; CHECK-NEXT: [[R:%.*]] = add i16 [[Y8_NEG]], [[X8]]
; CHECK-NEXT: [[TMP1:%.*]] = sub i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = shl i16 [[TMP1]], 3
; CHECK-NEXT: ret i16 [[R]]
;
%x8 = mul nuw i16 %x, 8
@ -1557,9 +1553,8 @@ define i16 @sub_nsw_mul_nuw(i16 %x, i16 %y) {
define i16 @sub_nuw_mul_nuw(i16 %x, i16 %y) {
; CHECK-LABEL: @sub_nuw_mul_nuw(
; CHECK-NEXT: [[X8:%.*]] = shl nuw i16 [[X:%.*]], 4
; CHECK-NEXT: [[Y8_NEG:%.*]] = mul i16 [[Y:%.*]], -16
; CHECK-NEXT: [[R:%.*]] = add i16 [[Y8_NEG]], [[X8]]
; CHECK-NEXT: [[TMP1:%.*]] = sub nuw i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = shl nuw i16 [[TMP1]], 4
; CHECK-NEXT: ret i16 [[R]]
;
%x8 = mul nuw i16 %x, 16
@ -1570,9 +1565,8 @@ define i16 @sub_nuw_mul_nuw(i16 %x, i16 %y) {
define i16 @sub_mul_nuw(i16 %x, i16 %y) {
; CHECK-LABEL: @sub_mul_nuw(
; CHECK-NEXT: [[X8:%.*]] = shl nuw i16 [[X:%.*]], 5
; CHECK-NEXT: [[Y8_NEG:%.*]] = mul i16 [[Y:%.*]], -32
; CHECK-NEXT: [[R:%.*]] = add i16 [[Y8_NEG]], [[X8]]
; CHECK-NEXT: [[TMP1:%.*]] = sub i16 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[R:%.*]] = shl i16 [[TMP1]], 5
; CHECK-NEXT: ret i16 [[R]]
;
%x8 = mul nuw i16 %x, 32