[ARM] Code size optimisation to lower udiv+urem to udiv+mls instead of a

library call to __aeabi_uidivmod. This is an improved implementation of
r280808, see also D24133, that got reverted because isel was stuck in a loop.
That was caused by the optimisation incorrectly triggering on i64 ints, which
shouldn't happen because there is no 64bit hwdiv support; that put isel's type
legalization and this optimisation in a loop. A native ARM compiler and testing
now shows that this is fixed.

Patch mostly by Pablo Barrio.

Differential Revision: https://reviews.llvm.org/D25077

llvm-svn: 283098

1 files changed, 72 insertions, 0 deletions

diff --git a/llvm/test/CodeGen/ARM/urem-opt-size.ll b/llvm/test/CodeGen/ARM/urem-opt-size.ll
index 7f1cd43bc4e..bcc53604959 100644
--- a/llvm/test/CodeGen/ARM/urem-opt-size.ll
+++ b/llvm/test/CodeGen/ARM/urem-opt-size.ll
@@ -3,7 +3,12 @@
 ; expanded to a sequence of umull, lsrs, muls and sub instructions, but
 ; just a call to __aeabi_uidivmod.
 ;
+; When the processor features hardware division, UDIV + UREM can be turned
+; into UDIV + MLS. This prevents the library function __aeabi_uidivmod to be
+; pulled into the binary. The test uses ARMv7-M.
+;
 ; RUN: llc -mtriple=armv7a-eabi -mattr=-neon -verify-machineinstrs %s -o - | FileCheck %s
+; RUN: llc -mtriple=thumbv7m-eabi -verify-machineinstrs %s -o - | FileCheck %s -check-prefix=V7M
 
 target datalayout = "e-m:e-p:32:32-i64:64-v128:64:128-a:0:32-n32-S64"
 target triple = "thumbv7m-arm-none-eabi"
@@ -28,11 +33,16 @@ entry:
   ret i32 %div
 }
 
+; Test for unsigned remainder
 define i32 @foo3() local_unnamed_addr #0 {
 entry:
 ; CHECK-LABEL: foo3:
 ; CHECK: __aeabi_uidivmod
 ; CHECK-NOT: umull
+; V7M-LABEL: foo3:
+; V7M: udiv [[R2:r[0-9]+]], [[R0:r[0-9]+]], [[R1:r[0-9]+]]
+; V7M: mls {{r[0-9]+}}, [[R2]], [[R1]], [[R0]]
+; V7M-NOT: __aeabi_uidivmod
   %call = tail call i32 bitcast (i32 (...)* @GetValue to i32 ()*)()
   %rem = urem i32 %call, 1000000
   %cmp = icmp eq i32 %rem, 0
@@ -40,6 +50,68 @@ entry:
   ret i32 %conv
 }
 
+; Test for signed remainder
+define i32 @foo4() local_unnamed_addr #0 {
+entry:
+; CHECK-LABEL: foo4:
+; CHECK:__aeabi_idivmod
+; V7M-LABEL: foo4:
+; V7M: sdiv [[R2:r[0-9]+]], [[R0:r[0-9]+]], [[R1:r[0-9]+]]
+; V7M: mls {{r[0-9]+}}, [[R2]], [[R1]], [[R0]]
+; V7M-NOT: __aeabi_idivmod
+  %call = tail call i32 bitcast (i32 (...)* @GetValue to i32 ()*)()
+  %rem = srem i32 %call, 1000000
+  ret i32 %rem
+}
+
+; Check that doing a sdiv+srem has the same effect as only the srem,
+; as the division needs to be computed anyway in order to calculate
+; the remainder (i.e. make sure we don't end up with two divisions).
+define i32 @foo5() local_unnamed_addr #0 {
+entry:
+; CHECK-LABEL: foo5:
+; CHECK:__aeabi_idivmod
+; V7M-LABEL: foo5:
+; V7M: sdiv [[R2:r[0-9]+]], [[R0:r[0-9]+]], [[R1:r[0-9]+]]
+; V7M-NOT: sdiv
+; V7M: mls {{r[0-9]+}}, [[R2]], [[R1]], [[R0]]
+; V7M-NOT: __aeabi_idivmod
+  %call = tail call i32 bitcast (i32 (...)* @GetValue to i32 ()*)()
+  %div = sdiv i32 %call, 1000000
+  %rem = srem i32 %call, 1000000
+  %add = add i32 %div, %rem
+  ret i32 %add
+}
+
+; An early version of this patch caused isel to hang. The reason
+; was that it shouldn't do the rewrite for i64 because that's not
+; supported by hardware. Isel was stuck in a loop with type
+; legalization and this optimisation.
+; Function Attrs: norecurse nounwind
+define i64 @isel_dont_hang(i32 %bar) local_unnamed_addr #4 {
+entry:
+; CHECK-LABEL: isel_dont_hang:
+; CHECK: __aeabi_uldivmod
+  %temp.0 = sext i32 %bar to i64
+  %mul83 = shl i64 %temp.0, 1
+  %add84 = add i64 %temp.0, 2
+  %div85 = udiv i64 %mul83, %add84
+  ret i64 %div85
+}
+
+; i16 types are promoted to i32, and we expect a normal udiv here:
+define i16 @isel_dont_hang_2(i16 %bar) local_unnamed_addr #4 {
+entry:
+; CHECK-LABEL: isel_dont_hang_2:
+; CHECK: udiv
+; CHECK-NOT: __aeabi_
+  %mul83 = shl i16 %bar, 1
+  %add84 = add i16 %bar, 2
+  %div85 = udiv i16 %mul83, %add84
+  ret i16 %div85
+}
 declare i32 @GetValue(...) local_unnamed_addr
 
 attributes #0 = { minsize nounwind optsize }
+attributes #4 = { norecurse nounwind "correctly-rounded-divide-sqrt-fp-math"="false" "disable-tail-calls"="false" "less-precise-fpmad"="false" "no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf" "no-jump-tables"="false" "stack-protector-buffer-size"="8" "target-cpu"="cortex-a15" "target-features"="+dsp,+hwdiv,+hwdiv-arm,+neon,+vfp4" "use-soft-float"="false" }
+