[CodeGen] Don't blindly combine (fp_round (fp_round x)) to (fp_round x).
We used to do this DAG combine, but it's not always correct:
If the first fp_round isn't a value preserving truncation, it might
introduce a tie in the second fp_round, that wouldn't occur in the
single-step fp_round we want to fold to.
In other words, double rounding isn't the same as rounding.
Differential Revision: http://reviews.llvm.org/D7571
llvm-svn: 228911
diff --git a/llvm/test/CodeGen/AArch64/f16-convert.ll b/llvm/test/CodeGen/AArch64/f16-convert.ll
index 12412d4..d1f49a91 100644
--- a/llvm/test/CodeGen/AArch64/f16-convert.ll
+++ b/llvm/test/CodeGen/AArch64/f16-convert.ll
@@ -133,7 +133,8 @@
define void @store1(i16* nocapture %a, double %val) nounwind {
; CHECK-LABEL: store1:
-; CHECK-NEXT: fcvt h0, d0
+; CHECK-NEXT: fcvt s0, d0
+; CHECK-NEXT: fcvt h0, s0
; CHECK-NEXT: str h0, [x0]
; CHECK-NEXT: ret
@@ -158,7 +159,8 @@
define void @store3(i16* nocapture %a, i32 %i, double %val) nounwind {
; CHECK-LABEL: store3:
-; CHECK-NEXT: fcvt h0, d0
+; CHECK-NEXT: fcvt s0, d0
+; CHECK-NEXT: fcvt h0, s0
; CHECK-NEXT: str h0, [x0, w1, sxtw #1]
; CHECK-NEXT: ret
@@ -184,7 +186,8 @@
define void @store5(i16* nocapture %a, i64 %i, double %val) nounwind {
; CHECK-LABEL: store5:
-; CHECK-NEXT: fcvt h0, d0
+; CHECK-NEXT: fcvt s0, d0
+; CHECK-NEXT: fcvt h0, s0
; CHECK-NEXT: str h0, [x0, x1, lsl #1]
; CHECK-NEXT: ret
@@ -209,7 +212,8 @@
define void @store7(i16* nocapture %a, double %val) nounwind {
; CHECK-LABEL: store7:
-; CHECK-NEXT: fcvt h0, d0
+; CHECK-NEXT: fcvt s0, d0
+; CHECK-NEXT: fcvt h0, s0
; CHECK-NEXT: str h0, [x0, #20]
; CHECK-NEXT: ret
@@ -234,7 +238,8 @@
define void @store9(i16* nocapture %a, double %val) nounwind {
; CHECK-LABEL: store9:
-; CHECK-NEXT: fcvt h0, d0
+; CHECK-NEXT: fcvt s0, d0
+; CHECK-NEXT: fcvt h0, s0
; CHECK-NEXT: stur h0, [x0, #-20]
; CHECK-NEXT: ret
diff --git a/llvm/test/CodeGen/X86/fp-double-rounding.ll b/llvm/test/CodeGen/X86/fp-double-rounding.ll
new file mode 100644
index 0000000..030cb9a
--- /dev/null
+++ b/llvm/test/CodeGen/X86/fp-double-rounding.ll
@@ -0,0 +1,31 @@
+; RUN: llc < %s | FileCheck %s --check-prefix=CHECK --check-prefix=SAFE
+; RUN: llc < %s -enable-unsafe-fp-math | FileCheck %s --check-prefix=CHECK --check-prefix=UNSAFE
+
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64--"
+
+; CHECK-LABEL: double_rounding:
+; SAFE: callq __trunctfdf2
+; SAFE-NEXT: cvtsd2ss %xmm0
+; UNSAFE: callq __trunctfsf2
+; UNSAFE-NOT: cvt
+define void @double_rounding(fp128* %x, float* %f) {
+entry:
+ %0 = load fp128* %x, align 16
+ %1 = fptrunc fp128 %0 to double
+ %2 = fptrunc double %1 to float
+ store float %2, float* %f, align 4
+ ret void
+}
+
+; CHECK-LABEL: double_rounding_precise_first:
+; CHECK: fstps (%
+; CHECK-NOT: fstpl
+define void @double_rounding_precise_first(float* %f) {
+entry:
+ ; Hack, to generate a precise FP_ROUND to double
+ %precise = call double asm sideeffect "fld %st(0)", "={st(0)}"()
+ %0 = fptrunc double %precise to float
+ store float %0, float* %f, align 4
+ ret void
+}