[PATCH] D83101: [Scalarizer] Constant ExtractElement Hanlding

[Roman Lebedev via Phabricator via llvm-commits]

lebedev.ri created this revision.
lebedev.ri added reviewers: jdoerfert, bjope, arsenm, cameron.mcinally.
lebedev.ri added a project: LLVM.
Herald added subscribers: hiraditya, wdng.
lebedev.ri added a child revision: D83102: [Scalarizer] Constant InsertElement Hanlding.
lebedev.ri added a parent revision: D82970: [Scalarizer] Variable insert handling (PR46524).
lebedev.ri marked an inline comment as done.
jdoerfert accepted this revision.
jdoerfert added a comment.
This revision is now accepted and ready to land.

LGTM.



================
Comment at: llvm/test/Transforms/Scalarizer/basic.ll:611
+; Test that constant extracts are nicely scalarized
+define i32 @f24(<4 x i32> *%src, i32 %index) {
+; CHECK-LABEL: @f24(
----------------
Previously we'd end up with https://godbolt.org/z/HDKdqh
```
  %val0 = load <4 x i32>, <4 x i32>* %src, align 16
  %val0.i0 = extractelement <4 x i32> %val0, i32 0
  %val1.i0 = shl i32 1, %val0.i0
  %val0.i1 = extractelement <4 x i32> %val0, i32 1
  %val1.i1 = shl i32 2, %val0.i1
  %val0.i2 = extractelement <4 x i32> %val0, i32 2
  %val1.i2 = shl i32 3, %val0.i2
  %val0.i3 = extractelement <4 x i32> %val0, i32 3
  %val1.i3 = shl i32 4, %val0.i3
  %val1.upto0 = insertelement <4 x i32> undef, i32 %val1.i0, i32 0
  %val1.upto1 = insertelement <4 x i32> %val1.upto0, i32 %val1.i1, i32 1
  %val1.upto2 = insertelement <4 x i32> %val1.upto1, i32 %val1.i2, i32 2
  %val1 = insertelement <4 x i32> %val1.upto2, i32 %val1.i3, i32 3
  %val2 = extractelement <4 x i32> %val1, i32 3
  ret i32 %val2
```



It appears to be better IR-wise to aggressively scalarize it,
rather than relying on gathering it, and leaving it as-is.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D83101

Files:
  llvm/lib/Transforms/Scalar/Scalarizer.cpp
  llvm/test/Transforms/Scalarizer/basic.ll
  llvm/test/Transforms/Scalarizer/phi-unreachable-pred.ll


Index: llvm/test/Transforms/Scalarizer/phi-unreachable-pred.ll
===================================================================
--- llvm/test/Transforms/Scalarizer/phi-unreachable-pred.ll
+++ llvm/test/Transforms/Scalarizer/phi-unreachable-pred.ll
@@ -15,12 +15,7 @@
 ; CHECK-NEXT:    [[PHI_I1:%.*]] = phi i16 [ 1, [[ENTRY]] ], [ undef, [[FOR_COND]] ]
 ; CHECK-NEXT:    [[PHI_I2:%.*]] = phi i16 [ 1, [[ENTRY]] ], [ undef, [[FOR_COND]] ]
 ; CHECK-NEXT:    [[PHI_I3:%.*]] = phi i16 [ 1, [[ENTRY]] ], [ undef, [[FOR_COND]] ]
-; CHECK-NEXT:    [[PHI_UPTO0:%.*]] = insertelement <4 x i16> undef, i16 [[PHI_I0]], i32 0
-; CHECK-NEXT:    [[PHI_UPTO1:%.*]] = insertelement <4 x i16> [[PHI_UPTO0]], i16 [[PHI_I1]], i32 1
-; CHECK-NEXT:    [[PHI_UPTO2:%.*]] = insertelement <4 x i16> [[PHI_UPTO1]], i16 [[PHI_I2]], i32 2
-; CHECK-NEXT:    [[PHI:%.*]] = insertelement <4 x i16> [[PHI_UPTO2]], i16 [[PHI_I3]], i32 3
-; CHECK-NEXT:    [[EXTRACT:%.*]] = extractelement <4 x i16> [[PHI]], i32 0
-; CHECK-NEXT:    ret i16 [[EXTRACT]]
+; CHECK-NEXT:    ret i16 [[PHI_I0]]
 ;
 entry:
   br label %for.end
Index: llvm/test/Transforms/Scalarizer/basic.ll
===================================================================
--- llvm/test/Transforms/Scalarizer/basic.ll
+++ llvm/test/Transforms/Scalarizer/basic.ll
@@ -607,6 +607,20 @@
   ret i32 %val2
 }
 
+; Test that constant extracts are nicely scalarized
+define i32 @f24(<4 x i32> *%src, i32 %index) {
+; CHECK-LABEL: @f24(
+; CHECK: %src.i0 = bitcast <4 x i32>* %src to i32*
+; CHECK: %src.i3 = getelementptr i32, i32* %src.i0, i32 3
+; CHECK: %val0.i3 = load i32, i32* %src.i3, align 4
+; CHECK: %val2 = shl i32 4, %val0.i3
+; CHECK: ret i32 %val2
+  %val0 = load <4 x i32> , <4 x i32> *%src
+  %val1 = shl <4 x i32> <i32 1, i32 2, i32 3, i32 4>, %val0
+  %val2 = extractelement <4 x i32> %val1, i32 3
+  ret i32 %val2
+}
+
 !0 = !{ !"root" }
 !1 = !{ !"set1", !0 }
 !2 = !{ !"set2", !0 }
Index: llvm/lib/Transforms/Scalar/Scalarizer.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/Scalarizer.cpp
+++ llvm/lib/Transforms/Scalar/Scalarizer.cpp
@@ -778,9 +778,6 @@
 }
 
 bool ScalarizerVisitor::visitExtractElementInst(ExtractElementInst &EEI) {
-  if (!ScalarizeVariableInsertExtract)
-    return false;
-
   VectorType *VT = dyn_cast<VectorType>(EEI.getOperand(0)->getType());
   if (!VT)
     return false;
@@ -789,7 +786,14 @@
   IRBuilder<> Builder(&EEI);
   Scatterer Op0 = scatter(&EEI, EEI.getOperand(0));
   Value *ExtIdx = EEI.getOperand(1);
-  if (isa<ConstantInt>(ExtIdx))
+
+  if (auto *CI = dyn_cast<ConstantInt>(ExtIdx)) {
+    Value *Res = Op0[CI->getValue().getZExtValue()];
+    gather(&EEI, {Res});
+    return true;
+  }
+
+  if (!ScalarizeVariableInsertExtract)
     return false;
 
   Value *Res = UndefValue::get(VT->getElementType());


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