[llvm-branch-commits] [llvm] release/23.x: [Matrix] De-duplicate reshaped matrixes used as incoming values for phi. (#211210) (PR #211498)

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<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: llvmbot

<details>
<summary>Changes</summary>

Backport 0e78045

Requested by: @<!-- -->fhahn

---
Full diff: https://github.com/llvm/llvm-project/pull/211498.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp (+7-1) 
- (modified) llvm/test/Transforms/LowerMatrixIntrinsics/phi.ll (+34) 


``````````diff
diff --git a/llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp b/llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp
index fc5313b2d868f..1e363437348f9 100644
--- a/llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp
+++ b/llvm/lib/Transforms/Scalar/LowerMatrixIntrinsics.cpp
@@ -2397,6 +2397,9 @@ class LowerMatrixIntrinsics {
     Builder.SetInsertPoint(BlockIP);
     MatrixTy PhiM = getMatrix(Inst, SI, Builder);
 
+    // Cache the reshaped columns per incoming block, so that a block listed
+    // more than once contributes identical incoming values to the new PHIs.
+    SmallDenseMap<BasicBlock *, MatrixTy> ReshapedIncoming;
     for (auto [IncomingV, IncomingB] :
          llvm::zip_equal(Inst->incoming_values(), Inst->blocks())) {
       // getMatrix() may insert some instructions to help with reshaping. The
@@ -2407,7 +2410,10 @@ class LowerMatrixIntrinsics {
         if (auto MaybeIP = IncomingInst->getInsertionPointAfterDef())
           Builder.SetInsertPoint(*MaybeIP);
 
-      MatrixTy OpM = getMatrix(IncomingV, SI, Builder);
+      auto [It, Inserted] = ReshapedIncoming.try_emplace(IncomingB);
+      if (Inserted)
+        It->second = getMatrix(IncomingV, SI, Builder);
+      const MatrixTy &OpM = It->second;
 
       for (unsigned VI = 0, VE = PhiM.getNumVectors(); VI != VE; ++VI) {
         PHINode *NewPHI = cast<PHINode>(PhiM.getVector(VI));
diff --git a/llvm/test/Transforms/LowerMatrixIntrinsics/phi.ll b/llvm/test/Transforms/LowerMatrixIntrinsics/phi.ll
index a8e71666421b4..2110d72951f10 100644
--- a/llvm/test/Transforms/LowerMatrixIntrinsics/phi.ll
+++ b/llvm/test/Transforms/LowerMatrixIntrinsics/phi.ll
@@ -861,3 +861,37 @@ exit:
   %phi = phi <4 x float> [ %inv, %cont ], [ %t, %bb ]
   ret <4 x float> %phi
 }
+
+define <4 x float> @matrix_phi_duplicate_predecessor(ptr %arg, i32 %sw) {
+; CHECK-LABEL: @matrix_phi_duplicate_predecessor(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[SPLIT:%.*]] = load <2 x float>, ptr [[ARG:%.*]], align 16
+; CHECK-NEXT:    [[VEC_GEP:%.*]] = getelementptr inbounds float, ptr [[ARG]], i64 2
+; CHECK-NEXT:    [[SPLIT3:%.*]] = load <2 x float>, ptr [[VEC_GEP]], align 8
+; CHECK-NEXT:    switch i32 [[SW:%.*]], label [[BB:%.*]] [
+; CHECK-NEXT:      i32 0, label [[EXIT:%.*]]
+; CHECK-NEXT:      i32 1, label [[EXIT]]
+; CHECK-NEXT:    ]
+; CHECK:       bb:
+; CHECK-NEXT:    br label [[EXIT]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[PHI1:%.*]] = phi <2 x float> [ [[SPLIT]], [[ENTRY:%.*]] ], [ [[SPLIT]], [[ENTRY]] ], [ zeroinitializer, [[BB]] ]
+; CHECK-NEXT:    [[PHI2:%.*]] = phi <2 x float> [ [[SPLIT3]], [[ENTRY]] ], [ [[SPLIT3]], [[ENTRY]] ], [ zeroinitializer, [[BB]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = shufflevector <2 x float> [[PHI1]], <2 x float> [[PHI2]], <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:    ret <4 x float> [[TMP0]]
+;
+entry:
+  %m = load <4 x float>, ptr %arg
+  switch i32 %sw, label %bb [
+  i32 0, label %exit
+  i32 1, label %exit
+  ]
+
+bb:
+  %t = call <4 x float> @llvm.matrix.transpose.v4f32(<4 x float> zeroinitializer, i32 2, i32 2)
+  br label %exit
+
+exit:
+  %phi = phi <4 x float> [ %m, %entry ], [ %m, %entry ], [ %t, %bb ]
+  ret <4 x float> %phi
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/211498