Subzero: Fix a register allocation issue for "advanced phi lowering".

tests_lit/llvm2ice_tests/phi.ll

Index: tests_lit/llvm2ice_tests/phi.ll
diff --git a/tests_lit/llvm2ice_tests/phi.ll b/tests_lit/llvm2ice_tests/phi.ll
index abdc1b3beaf4068521811519515b4b7da516a354..4e75850c2115a664eb5138f608c5f991b9994cc5 100644
--- a/tests_lit/llvm2ice_tests/phi.ll
+++ b/tests_lit/llvm2ice_tests/phi.ll
@@ -4,6 +4,8 @@
 
 ; RUN: %p2i -i %s --filetype=obj --disassemble --args -O2 --phi-edge-split=0 \
 ; RUN:   | FileCheck %s
+; RUN: %p2i -i %s --filetype=obj --disassemble --args -O2 --phi-edge-split=1 \
+; RUN:   | FileCheck --check-prefix=SPLIT %s
 
 define internal i32 @testPhi1(i32 %arg) {
 entry:
@@ -99,3 +101,59 @@ exit:
 ; CHECK: jne
 ; CHECK: mov DWORD PTR [[ADDR]]
 ; CHECK: pop [[EBX]]
+
+; Test of "advanced phi lowering" with undef phi arg (integer vector).
+define internal <4 x i32> @test_split_undef_int_vec(<4 x i32> %arg, i32 %cond) {
+entry:
+  %cmp = icmp eq i32 %cond, 0
+  br i1 %cmp, label %eq, label %exit
+eq:
+  br label %exit
+exit:
+  %merge = phi <4 x i32> [ %arg, %entry ], [ undef, %eq ]
+  ret <4 x i32> %merge
+}
+; SPLIT-LABEL: test_split_undef_int_vec
+; SPLIT: pxor
+
+; Test of "advanced phi lowering" with undef phi arg (float vector).
+define internal <4 x float> @test_split_undef_float_vec(<4 x float> %arg, i32 %cond) {
+entry:
+  %cmp = icmp eq i32 %cond, 0
+  br i1 %cmp, label %eq, label %exit
+eq:
+  br label %exit
+exit:
+  %merge = phi <4 x float> [ %arg, %entry ], [ undef, %eq ]
+  ret <4 x float> %merge
+}
+; SPLIT-LABEL: test_split_undef_float_vec
+; SPLIT: pxor
+
+; Test of "advanced phi lowering" with undef phi arg (integer scalar).
+define internal i32 @test_split_undef_int_scalar(i32 %arg, i32 %cond) {
+entry:
+  %cmp = icmp eq i32 %cond, 0
+  br i1 %cmp, label %eq, label %exit
+eq:
+  br label %exit
+exit:
+  %merge = phi i32 [ %arg, %entry ], [ undef, %eq ]
+  ret i32 %merge
+}
+; SPLIT-LABEL: test_split_undef_int_scalar
+; SPLIT: mov {{.*}},0x0
+
+; Test of "advanced phi lowering" with undef phi arg (float scalar).
+define internal float @test_split_undef_float_scalar(float %arg, i32 %cond) {
+entry:
+  %cmp = icmp eq i32 %cond, 0
+  br i1 %cmp, label %eq, label %exit
+eq:
+  br label %exit
+exit:
+  %merge = phi float [ %arg, %entry ], [ undef, %eq ]
+  ret float %merge
+}
+; SPLIT-LABEL: test_split_undef_float_scalar
+; SPLIT: movss {{.*}},DWORD PTR