[llvm] 25a97c3 - [InstCombine] visitCallInst - retain undefs in vector funnel shift amounts

[Simon Pilgrim via llvm-commits]

Author: Simon Pilgrim
Date: 2020-10-14T14:38:21+01:00
New Revision: 25a97c3a43d7bc469ec67dd4e901a507b9b11116

URL: https://github.com/llvm/llvm-project/commit/25a97c3a43d7bc469ec67dd4e901a507b9b11116
DIFF: https://github.com/llvm/llvm-project/commit/25a97c3a43d7bc469ec67dd4e901a507b9b11116.diff

LOG: [InstCombine] visitCallInst - retain undefs in vector funnel shift amounts

By always performing a modulo on the shift amount constants this was causing undef amounts being replaced with zero, meaning we were losing funnel shift by splat (with undef) patterns.

Tweaked the shift amount bounds check to support (passthrough) undefs, and use Constant::mergeUndefsWith to preserve the undefs after folding.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
    llvm/test/Transforms/InstCombine/funnel.ll
    llvm/test/Transforms/InstCombine/rotate.ll

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index c06965780929..74165169cab9 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -885,15 +885,15 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
     Constant *ShAmtC;
     if (match(II->getArgOperand(2), m_Constant(ShAmtC)) &&
         !isa<ConstantExpr>(ShAmtC) && !ShAmtC->containsConstantExpression()) {
-      // Canonicalize a shift amount constant operand to modulo the bit-width.
       Constant *WidthC = ConstantInt::get(Ty, BitWidth);
-      Constant *ModuloC = ConstantExpr::getURem(ShAmtC, WidthC);
-      if (ModuloC != ShAmtC)
-        return replaceOperand(*II, 2, ModuloC);
 
-      assert(ConstantExpr::getICmp(ICmpInst::ICMP_UGT, WidthC, ShAmtC) ==
-                 ConstantInt::getTrue(CmpInst::makeCmpResultType(Ty)) &&
-             "Shift amount expected to be modulo bitwidth");
+      // Canonicalize a shift amount constant operand to modulo the bit-width.
+      if (!match(ShAmtC, m_SpecificInt_ICMP(ICmpInst::ICMP_ULT,
+                                            APInt(BitWidth, BitWidth)))) {
+        Constant *ModuloC = ConstantExpr::getURem(ShAmtC, WidthC);
+        ModuloC = Constant::mergeUndefsWith(ModuloC, ShAmtC);
+        return replaceOperand(*II, 2, ModuloC);
+      }
 
       // Canonicalize funnel shift right by constant to funnel shift left. This
       // is not entirely arbitrary. For historical reasons, the backend may

diff  --git a/llvm/test/Transforms/InstCombine/funnel.ll b/llvm/test/Transforms/InstCombine/funnel.ll
index 5c9427973430..7c60f1516084 100644
--- a/llvm/test/Transforms/InstCombine/funnel.ll
+++ b/llvm/test/Transforms/InstCombine/funnel.ll
@@ -116,7 +116,7 @@ define <2 x i32> @fshr_v2i32_constant_nonsplat(<2 x i32> %x, <2 x i32> %y) {
 
 define <2 x i32> @fshr_v2i32_constant_nonsplat_undef0(<2 x i32> %x, <2 x i32> %y) {
 ; CHECK-LABEL: @fshr_v2i32_constant_nonsplat_undef0(
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[Y:%.*]], <2 x i32> [[X:%.*]], <2 x i32> <i32 0, i32 13>)
+; CHECK-NEXT:    [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[Y:%.*]], <2 x i32> [[X:%.*]], <2 x i32> <i32 undef, i32 13>)
 ; CHECK-NEXT:    ret <2 x i32> [[R]]
 ;
   %shr = lshr <2 x i32> %x, <i32 undef, i32 19>
@@ -127,7 +127,7 @@ define <2 x i32> @fshr_v2i32_constant_nonsplat_undef0(<2 x i32> %x, <2 x i32> %y
 
 define <2 x i32> @fshr_v2i32_constant_nonsplat_undef1(<2 x i32> %x, <2 x i32> %y) {
 ; CHECK-LABEL: @fshr_v2i32_constant_nonsplat_undef1(
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[Y:%.*]], <2 x i32> [[X:%.*]], <2 x i32> <i32 15, i32 0>)
+; CHECK-NEXT:    [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[Y:%.*]], <2 x i32> [[X:%.*]], <2 x i32> <i32 15, i32 undef>)
 ; CHECK-NEXT:    ret <2 x i32> [[R]]
 ;
   %shr = lshr <2 x i32> %x, <i32 17, i32 19>
@@ -149,7 +149,7 @@ define <2 x i36> @fshl_v2i36_constant_nonsplat(<2 x i36> %x, <2 x i36> %y) {
 
 define <3 x i36> @fshl_v3i36_constant_nonsplat_undef0(<3 x i36> %x, <3 x i36> %y) {
 ; CHECK-LABEL: @fshl_v3i36_constant_nonsplat_undef0(
-; CHECK-NEXT:    [[R:%.*]] = call <3 x i36> @llvm.fshl.v3i36(<3 x i36> [[X:%.*]], <3 x i36> [[Y:%.*]], <3 x i36> <i36 21, i36 11, i36 0>)
+; CHECK-NEXT:    [[R:%.*]] = call <3 x i36> @llvm.fshl.v3i36(<3 x i36> [[X:%.*]], <3 x i36> [[Y:%.*]], <3 x i36> <i36 21, i36 11, i36 undef>)
 ; CHECK-NEXT:    ret <3 x i36> [[R]]
 ;
   %shl = shl <3 x i36> %x, <i36 21, i36 11, i36 undef>

diff  --git a/llvm/test/Transforms/InstCombine/rotate.ll b/llvm/test/Transforms/InstCombine/rotate.ll
index 270d778a3091..c911f290a9d8 100644
--- a/llvm/test/Transforms/InstCombine/rotate.ll
+++ b/llvm/test/Transforms/InstCombine/rotate.ll
@@ -138,7 +138,7 @@ define <2 x i32> @rotr_v2i32_constant_nonsplat(<2 x i32> %x) {
 
 define <2 x i32> @rotr_v2i32_constant_nonsplat_undef0(<2 x i32> %x) {
 ; CHECK-LABEL: @rotr_v2i32_constant_nonsplat_undef0(
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[X:%.*]], <2 x i32> [[X]], <2 x i32> <i32 0, i32 19>)
+; CHECK-NEXT:    [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[X:%.*]], <2 x i32> [[X]], <2 x i32> <i32 undef, i32 19>)
 ; CHECK-NEXT:    ret <2 x i32> [[R]]
 ;
   %shl = shl <2 x i32> %x, <i32 undef, i32 19>
@@ -149,7 +149,7 @@ define <2 x i32> @rotr_v2i32_constant_nonsplat_undef0(<2 x i32> %x) {
 
 define <2 x i32> @rotr_v2i32_constant_nonsplat_undef1(<2 x i32> %x) {
 ; CHECK-LABEL: @rotr_v2i32_constant_nonsplat_undef1(
-; CHECK-NEXT:    [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[X:%.*]], <2 x i32> [[X]], <2 x i32> <i32 17, i32 0>)
+; CHECK-NEXT:    [[R:%.*]] = call <2 x i32> @llvm.fshl.v2i32(<2 x i32> [[X:%.*]], <2 x i32> [[X]], <2 x i32> <i32 17, i32 undef>)
 ; CHECK-NEXT:    ret <2 x i32> [[R]]
 ;
   %shl = shl <2 x i32> %x, <i32 17, i32 19>
@@ -171,7 +171,7 @@ define <2 x i36> @rotl_v2i36_constant_nonsplat(<2 x i36> %x) {
 
 define <3 x i36> @rotl_v3i36_constant_nonsplat_undef0(<3 x i36> %x) {
 ; CHECK-LABEL: @rotl_v3i36_constant_nonsplat_undef0(
-; CHECK-NEXT:    [[R:%.*]] = call <3 x i36> @llvm.fshl.v3i36(<3 x i36> [[X:%.*]], <3 x i36> [[X]], <3 x i36> <i36 21, i36 11, i36 0>)
+; CHECK-NEXT:    [[R:%.*]] = call <3 x i36> @llvm.fshl.v3i36(<3 x i36> [[X:%.*]], <3 x i36> [[X]], <3 x i36> <i36 21, i36 11, i36 undef>)
 ; CHECK-NEXT:    ret <3 x i36> [[R]]
 ;
   %shl = shl <3 x i36> %x, <i36 21, i36 11, i36 undef>