Fix shuffle feeding shuffle with undef literal (#4883)

When folding a vector shuffle with an undef literal, it is possible that the literal is adjusted so that it will then be interpreted as an index into the input operands. This is fixed by special casing that case, and not adjusting those operands. Fixes #4859
KhronosGroup · Aug 10, 2022 · 0a43a84 · 0a43a84
1 parent 0ebcdc4
commit 0a43a84
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diff --git a/source/opt/folding_rules.cpp b/source/opt/folding_rules.cpp
@@ -2748,7 +2748,8 @@ FoldingRule VectorShuffleFeedingShuffle() {
 
       if (adjustment != 0) {
         for (uint32_t i = 2; i < new_operands.size(); i++) {
-          if (inst->GetSingleWordInOperand(i) >= op0_length) {
+          uint32_t operand = inst->GetSingleWordInOperand(i);
+          if (operand >= op0_length && operand != undef_literal) {
             new_operands[i].words[0] -= adjustment;
           }
         }

diff --git a/test/opt/fold_test.cpp b/test/opt/fold_test.cpp
@@ -7963,6 +7963,27 @@ ::testing::Values(
             "%9 = OpVectorShuffle %v4double %7 %8 2 0 1 4294967295\n" +
             "OpReturn\n" +
             "OpFunctionEnd",
+        9, true),
+    // Test case 14: Shuffle with undef literal and change size of first input vector.
+    InstructionFoldingCase<bool>(
+        Header() +
+            "; CHECK: [[double:%\\w+]] = OpTypeFloat 64\n" +
+            "; CHECK: [[v4double:%\\w+]] = OpTypeVector [[double]] 2\n" +
+            "; CHECK: OpVectorShuffle\n" +
+            "; CHECK: OpVectorShuffle {{%\\w+}} %5 %7 0 1 4 4294967295\n" +
+            "; CHECK: OpReturn\n" +
+            "%main = OpFunction %void None %void_func\n" +
+            "%main_lab = OpLabel\n" +
+            "%2 = OpVariable %_ptr_v4double Function\n" +
+            "%3 = OpVariable %_ptr_v4double Function\n" +
+            "%4 = OpVariable %_ptr_v4double Function\n" +
+            "%5 = OpLoad %v4double %2\n" +
+            "%6 = OpLoad %v4double %3\n" +
+            "%7 = OpLoad %v4double %4\n" +
+            "%8 = OpVectorShuffle %v2double %5 %5 0 1\n" +
+            "%9 = OpVectorShuffle %v4double %8 %7 0 1 2 4294967295\n" +
+            "OpReturn\n" +
+            "OpFunctionEnd",
         9, true)
 ));