Subzero: Always be sure x87 FP stack is emptied after a call.

src/IceTargetLoweringX8632.cpp

@@ -1900,9 +1900,12 @@ void TargetX8632::lowerCall(const InstCall *Instr) {
   } else if (Dest->getType() == IceType_f32 || Dest->getType() == IceType_f64) {
     // Special treatment for an FP function which returns its result in
     // st(0).
-    _fstp(Dest);
     // If Dest ends up being a physical xmm register, the fstp emit code
     // will route st(0) through a temporary stack slot.
+    _fstp(Dest);
+    // Create a fake use of Dest in case it actually isn't used,
+    // because st(0) still needs to be popped.
+    Context.insert(InstFakeUse::create(Func, Dest));
   }
 }
 

tests_lit/llvm2ice_tests/fpcall.ll

+; Test that for calls returning a floating-point value, the calling
+; ABI with respect to the x87 floating point stack is honored.  In
+; particular, the top-of-stack must be popped regardless of whether
+; its value is used.
+
+; RUN: %llvm2ice -O2 --verbose none %s \
+; RUN:   | llvm-mc -triple=i686-none-nacl -x86-asm-syntax=intel -filetype=obj \
+; RUN:   | llvm-objdump -d --symbolize -x86-asm-syntax=intel - | FileCheck %s
+; RUN: %llvm2ice -Om1 --verbose none %s \
+; RUN:   | llvm-mc -triple=i686-none-nacl -x86-asm-syntax=intel -filetype=obj \
+; RUN:   | llvm-objdump -d --symbolize -x86-asm-syntax=intel - | FileCheck %s
+; RUN: %llvm2ice --verbose none %s | FileCheck --check-prefix=ERRORS %s
+; RUN: %llvm2iceinsts %s | %szdiff %s | FileCheck --check-prefix=DUMP %s
+; RUN: %llvm2iceinsts --pnacl %s | %szdiff %s \
+; RUN:                           | FileCheck --check-prefix=DUMP %s
+
+define float @dummy() {
+entry:
+  ret float 0.000000e+00
+}
+; CHECK-LABEL: dummy
+
+; The call is ignored, but the top of the FP stack still needs to be
+; popped.
+define i32 @ignored_fp_call() {
+entry:
+  %ignored = call float @dummy()
+  ret i32 0
+}
+; CHECK-LABEL: ignored_fp_call
+; CHECK: call dummy
+; CHECK: fstp
+
+; The top of the FP stack is popped and subsequently used.
+define i32 @converted_fp_call() {
+entry:
+  %fp = call float @dummy()
+  %ret = fptosi float %fp to i32
+  ret i32 %ret
+}
+; CHECK-LABEL: converted_fp_call
+; CHECK: call dummy
+; CHECK: fstp
+; CHECK: cvttss2si
+
+; The top of the FP stack is ultimately passed through as the return
+; value.  Note: the translator could optimized by not popping and
+; re-pushing, in which case the test would need to be changed.
+define float @returned_fp_call() {
+entry:
+  %fp = call float @dummy()
+  ret float %fp
+}
+; CHECK-LABEL: returned_fp_call
+; CHECK: call dummy
+; CHECK: fstp
+; CHECK: fld
+
+; ERRORS-NOT: ICE translation error
+; DUMP-NOT: SZ