[PATCH] D88402: [InstCombine] matchRotate - allow undef in uniform constant rotation amounts (PR46895)

[Simon Pilgrim via Phabricator via llvm-commits]

RKSimon created this revision.
RKSimon added reviewers: nikic, lebedev.ri, spatel.
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An extension to D87452 <https://reviews.llvm.org/D87452>, we can safely permit undefs in the uniform/splat detection

https://alive2.llvm.org/ce/z/nT-ptN


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D88402

Files:
  llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
  llvm/test/Transforms/InstCombine/rotate.ll


Index: llvm/test/Transforms/InstCombine/rotate.ll
===================================================================
--- llvm/test/Transforms/InstCombine/rotate.ll
+++ llvm/test/Transforms/InstCombine/rotate.ll
@@ -67,9 +67,7 @@
 
 define <2 x i16> @rotl_v2i16_constant_splat_undef0(<2 x i16> %x) {
 ; CHECK-LABEL: @rotl_v2i16_constant_splat_undef0(
-; CHECK-NEXT:    [[SHL:%.*]] = shl <2 x i16> [[X:%.*]], <i16 undef, i16 1>
-; CHECK-NEXT:    [[SHR:%.*]] = lshr <2 x i16> [[X]], <i16 15, i16 15>
-; CHECK-NEXT:    [[R:%.*]] = or <2 x i16> [[SHL]], [[SHR]]
+; CHECK-NEXT:    [[R:%.*]] = call <2 x i16> @llvm.fshl.v2i16(<2 x i16> [[X:%.*]], <2 x i16> [[X]], <2 x i16> <i16 0, i16 1>)
 ; CHECK-NEXT:    ret <2 x i16> [[R]]
 ;
   %shl = shl <2 x i16> %x, <i16 undef, i16 1>
@@ -80,9 +78,7 @@
 
 define <2 x i16> @rotl_v2i16_constant_splat_undef1(<2 x i16> %x) {
 ; CHECK-LABEL: @rotl_v2i16_constant_splat_undef1(
-; CHECK-NEXT:    [[SHL:%.*]] = shl <2 x i16> [[X:%.*]], <i16 1, i16 1>
-; CHECK-NEXT:    [[SHR:%.*]] = lshr <2 x i16> [[X]], <i16 15, i16 undef>
-; CHECK-NEXT:    [[R:%.*]] = or <2 x i16> [[SHL]], [[SHR]]
+; CHECK-NEXT:    [[R:%.*]] = call <2 x i16> @llvm.fshl.v2i16(<2 x i16> [[X:%.*]], <2 x i16> [[X]], <2 x i16> <i16 1, i16 1>)
 ; CHECK-NEXT:    ret <2 x i16> [[R]]
 ;
   %shl = shl <2 x i16> %x, <i16 1, i16 1>
@@ -106,9 +102,7 @@
 
 define <2 x i17> @rotr_v2i17_constant_splat_undef0(<2 x i17> %x) {
 ; CHECK-LABEL: @rotr_v2i17_constant_splat_undef0(
-; CHECK-NEXT:    [[SHL:%.*]] = shl <2 x i17> [[X:%.*]], <i17 12, i17 undef>
-; CHECK-NEXT:    [[SHR:%.*]] = lshr <2 x i17> [[X]], <i17 undef, i17 5>
-; CHECK-NEXT:    [[R:%.*]] = or <2 x i17> [[SHR]], [[SHL]]
+; CHECK-NEXT:    [[R:%.*]] = call <2 x i17> @llvm.fshl.v2i17(<2 x i17> [[X:%.*]], <2 x i17> [[X]], <2 x i17> <i17 0, i17 12>)
 ; CHECK-NEXT:    ret <2 x i17> [[R]]
 ;
   %shl = shl <2 x i17> %x, <i17 12, i17 undef>
@@ -119,9 +113,7 @@
 
 define <2 x i17> @rotr_v2i17_constant_splat_undef1(<2 x i17> %x) {
 ; CHECK-LABEL: @rotr_v2i17_constant_splat_undef1(
-; CHECK-NEXT:    [[SHL:%.*]] = shl <2 x i17> [[X:%.*]], <i17 12, i17 undef>
-; CHECK-NEXT:    [[SHR:%.*]] = lshr <2 x i17> [[X]], <i17 5, i17 undef>
-; CHECK-NEXT:    [[R:%.*]] = or <2 x i17> [[SHR]], [[SHL]]
+; CHECK-NEXT:    [[R:%.*]] = call <2 x i17> @llvm.fshl.v2i17(<2 x i17> [[X:%.*]], <2 x i17> [[X]], <2 x i17> <i17 12, i17 0>)
 ; CHECK-NEXT:    ret <2 x i17> [[R]]
 ;
   %shl = shl <2 x i17> %x, <i17 12, i17 undef>
Index: llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
===================================================================
--- llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
+++ llvm/lib/Transforms/InstCombine/InstCombineAndOrXor.cpp
@@ -2111,7 +2111,7 @@
     // Check for constant shift amounts that sum to the bitwidth.
     // TODO: Support non-uniform shift amounts.
     const APInt *LC, *RC;
-    if (match(L, m_APInt(LC)) && match(R, m_APInt(RC)))
+    if (match(L, m_APIntAllowUndef(LC)) && match(R, m_APIntAllowUndef(RC)))
       if (LC->ult(Width) && RC->ult(Width) && (*LC + *RC) == Width)
         return L;
 


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