llvm-mirror/test/CodeGen/AArch64/ftrunc.ll
Sanjay Patel 62ad0a5cf3 [DAGCombiner] restrict (float)((int) f) --> ftrunc with no-signed-zeros
As noted in the D44909 review, the transform from (fptosi+sitofp) to ftrunc 
can produce -0.0 where the original code does not:

#include <stdio.h>
  
int main(int argc) {
  float x;
  x = -0.8 * argc;
  printf("%f\n", (float)((int)x));
  return 0;
}

$ clang -O0 -mavx fp.c ; ./a.out 
0.000000
$ clang -O1 -mavx fp.c ; ./a.out 
-0.000000

Ideally, we'd use IR/node flags to predicate the transform, but the IR parser 
doesn't currently allow fast-math-flags on the cast instructions. So for now, 
just use the function attribute that corresponds to clang's "-fno-signed-zeros" 
option.

Differential Revision: https://reviews.llvm.org/D48085

llvm-svn: 335761
2018-06-27 18:16:40 +00:00

46 lines
1.1 KiB
LLVM

; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
; RUN: llc -mtriple=aarch64-unknown-unknown < %s | FileCheck %s
define float @trunc_unsigned_f32(float %x) #0 {
; CHECK-LABEL: trunc_unsigned_f32:
; CHECK: // %bb.0:
; CHECK-NEXT: frintz s0, s0
; CHECK-NEXT: ret
%i = fptoui float %x to i32
%r = uitofp i32 %i to float
ret float %r
}
define double @trunc_unsigned_f64(double %x) #0 {
; CHECK-LABEL: trunc_unsigned_f64:
; CHECK: // %bb.0:
; CHECK-NEXT: frintz d0, d0
; CHECK-NEXT: ret
%i = fptoui double %x to i64
%r = uitofp i64 %i to double
ret double %r
}
define float @trunc_signed_f32(float %x) #0 {
; CHECK-LABEL: trunc_signed_f32:
; CHECK: // %bb.0:
; CHECK-NEXT: frintz s0, s0
; CHECK-NEXT: ret
%i = fptosi float %x to i32
%r = sitofp i32 %i to float
ret float %r
}
define double @trunc_signed_f64(double %x) #0 {
; CHECK-LABEL: trunc_signed_f64:
; CHECK: // %bb.0:
; CHECK-NEXT: frintz d0, d0
; CHECK-NEXT: ret
%i = fptosi double %x to i64
%r = sitofp i64 %i to double
ret double %r
}
attributes #0 = { "no-signed-zeros-fp-math"="true" }