[ValueTracking] Strengthen impliesPoison reasoning

Split impliesPoison into two recursive walks, one over V, the
other over ValAssumedPoison. This allows us to reason about poison
implications in a number of additional cases that are important
in practice. This is a generalized form of D94859, which handles
the cmp to cmp implication in particular.

Differential Revision: https://reviews.llvm.org/D94866

1 files changed, 40 insertions, 0 deletions

diff --git a/llvm/unittests/Analysis/ValueTrackingTest.cpp b/llvm/unittests/Analysis/ValueTrackingTest.cpp
index 4b3b33b..f3240e0 100644
--- a/llvm/unittests/Analysis/ValueTrackingTest.cpp
+++ b/llvm/unittests/Analysis/ValueTrackingTest.cpp
@@ -748,6 +748,46 @@ TEST_F(ValueTrackingTest, impliesPoisonTest_AddNsw) {
   EXPECT_FALSE(impliesPoison(A2, A));
 }
 
+TEST_F(ValueTrackingTest, impliesPoisonTest_Cmp) {
+  parseAssembly("define void @test(i32 %x, i32 %y, i1 %c) {\n"
+                "  %A2 = icmp eq i32 %x, %y\n"
+                "  %A0 = icmp ult i32 %x, %y\n"
+                "  %A = or i1 %A0, %c\n"
+                "  ret void\n"
+                "}");
+  EXPECT_TRUE(impliesPoison(A2, A));
+}
+
+TEST_F(ValueTrackingTest, impliesPoisonTest_FCmpFMF) {
+  parseAssembly("define void @test(float %x, float %y, i1 %c) {\n"
+                "  %A2 = fcmp nnan oeq float %x, %y\n"
+                "  %A0 = fcmp olt float %x, %y\n"
+                "  %A = or i1 %A0, %c\n"
+                "  ret void\n"
+                "}");
+  EXPECT_FALSE(impliesPoison(A2, A));
+}
+
+TEST_F(ValueTrackingTest, impliesPoisonTest_AddSubSameOps) {
+  parseAssembly("define void @test(i32 %x, i32 %y, i1 %c) {\n"
+                "  %A2 = add i32 %x, %y\n"
+                "  %A = sub i32 %x, %y\n"
+                "  ret void\n"
+                "}");
+  EXPECT_TRUE(impliesPoison(A2, A));
+}
+
+TEST_F(ValueTrackingTest, impliesPoisonTest_MaskCmp) {
+  parseAssembly("define void @test(i32 %x, i32 %y, i1 %c) {\n"
+                "  %M2 = and i32 %x, 7\n"
+                "  %A2 = icmp eq i32 %M2, 1\n"
+                "  %M = and i32 %x, 15\n"
+                "  %A = icmp eq i32 %M, 3\n"
+                "  ret void\n"
+                "}");
+  EXPECT_TRUE(impliesPoison(A2, A));
+}
+
 TEST_F(ValueTrackingTest, ComputeNumSignBits_Shuffle_Pointers) {
   parseAssembly(
       "define <2 x i32*> @test(<2 x i32*> %x) {\n"