If the LHS of the FCMP is coming from a UIToFP instruction, then we don't want

to generate signed ICMP instructions to replace the FCMP. This would violate
the following:

define i1 @test1(i32 %val) {
  %1 = uitofp i32 %val to double
  %2 = fcmp ole double %1, 0.000000e+00
  ret i1 %2
}

would be transformed into:

define i1 @test1(i32 %val) {
  %1 = icmp slt i33 %val, 1
  ret i1 %1
}

which is obviously wrong. This patch modifes InstCombiner::FoldFCmp_IntToFP_Cst
to handle when the LHS comes from UIToFP.

llvm-svn: 58929

1 files changed, 46 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/2008-11-08-FCmp.ll b/llvm/test/Transforms/InstCombine/2008-11-08-FCmp.ll
new file mode 100644
index 00000000000..c088f3166fa
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/2008-11-08-FCmp.ll
@@ -0,0 +1,46 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis > %t
+; RUN: grep {icmp eq} %t
+; RUN: grep {ret i1 false} %t | count 2
+; RUN: grep {ret i1 true} %t | count 2
+; RUN: grep {icmp ne} %t
+; RUN: not grep {icmp slt} %t
+; PR3021
+
+; When inst combining an FCMP with the LHS coming from a uitofp instruction, we
+; can't lower it to signed ICMP instructions.
+
+define i1 @test1(i32 %val) {
+  %1 = uitofp i32 %val to double
+  %2 = fcmp ole double %1, 0.000000e+00
+  ret i1 %2
+}
+
+define i1 @test2(i32 %val) {
+  %1 = uitofp i32 %val to double
+  %2 = fcmp olt double %1, 0.000000e+00
+  ret i1 %2
+}
+
+define i1 @test3(i32 %val) {
+  %1 = uitofp i32 %val to double
+  %2 = fcmp oge double %1, 0.000000e+00
+  ret i1 %2
+}
+
+define i1 @test4(i32 %val) {
+  %1 = uitofp i32 %val to double
+  %2 = fcmp ogt double %1, 0.000000e+00
+  ret i1 %2
+}
+
+define i1 @test5(i32 %val) {
+  %1 = uitofp i32 %val to double
+  %2 = fcmp ogt double %1, -4.400000e+00
+  ret i1 %2
+}
+
+define i1 @test6(i32 %val) {
+  %1 = uitofp i32 %val to double
+  %2 = fcmp olt double %1, -4.400000e+00
+  ret i1 %2
+}