commit 0a43a84e02245cca40ce187d1e427a5d0b4f3d13
author Steven Perron <stevenperron@google.com> Wed Aug 10 09:04:35 2022 -0400
committer GitHub <noreply@github.com> Wed Aug 10 09:04:35 2022 -0400
tree b8d2b05a276b05719d6a86ad17ae5e7704a88196
parent 0ebcdc4d19de627023d538826672c816e3e90f32

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

source/opt/folding_rules.cpp

diff --git a/source/opt/folding_rules.cpp b/source/opt/folding_rules.cpp
index 2d778b9..3f10bd0 100644
--- a/source/opt/folding_rules.cpp
+++ b/source/opt/folding_rules.cpp
@@ -2748,7 +2748,8 @@
 
       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;
           }
         }

test/opt/fold_test.cpp

diff --git a/test/opt/fold_test.cpp b/test/opt/fold_test.cpp
index f6c94ca..a034e95 100644
--- a/test/opt/fold_test.cpp
+++ b/test/opt/fold_test.cpp
@@ -7963,6 +7963,27 @@
             "%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)
 ));