[llvm] 678b9c5 - [InstCombine] try difference-of-shifts factorization before negator

Sanjay Patel via llvm-commits llvm-commits at lists.llvm.org
Tue Nov 24 10:56:46 PST 2020 

Author: Sanjay Patel
Date: 2020-11-24T13:56:30-05:00
New Revision: 678b9c5dde0d119e91f5f905c3d9101cf8c514f9

URL: https://github.com/llvm/llvm-project/commit/678b9c5dde0d119e91f5f905c3d9101cf8c514f9
DIFF: https://github.com/llvm/llvm-project/commit/678b9c5dde0d119e91f5f905c3d9101cf8c514f9.diff

LOG: [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.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
    llvm/test/Transforms/InstCombine/sub-gep.ll
    llvm/test/Transforms/InstCombine/sub.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 9a6a790aefaf..bf356d0de94b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -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);
 

diff  --git a/llvm/test/Transforms/InstCombine/sub-gep.ll b/llvm/test/Transforms/InstCombine/sub-gep.ll
index d6ace8275c10..bc18608da7a5 100644
--- a/llvm/test/Transforms/InstCombine/sub-gep.ll
+++ b/llvm/test/Transforms/InstCombine/sub-gep.ll
@@ -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

diff  --git a/llvm/test/Transforms/InstCombine/sub.ll b/llvm/test/Transforms/InstCombine/sub.ll
index f325f8d09cf9..066085fc2535 100644
--- a/llvm/test/Transforms/InstCombine/sub.ll
+++ b/llvm/test/Transforms/InstCombine/sub.ll
@@ -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

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