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

Author: s-perron

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;
           }
         }

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)
 ));