Generate PPC early conditional returns

PowerPC has a conditional branch to the link register (return) instruction: BCLR.
This should be used any time when we'd otherwise have a conditional branch to a
return. This adds a small pass, PPCEarlyReturn, which runs just prior to the
branch selection pass (and, importantly, after block placement) to generate
these conditional returns when possible. It will also eliminate unconditional
branches to returns (these happen rarely; most of the time these have already
been tail duplicated by the time PPCEarlyReturn is invoked). This is a nice
optimization for small functions that do not maintain a stack frame.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@179026 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/PowerPC/early-ret.ll

@@ -0,0 +1,52 @@
+; RUN: llc < %s -mtriple=powerpc64-unknown-linux-gnu -mcpu=pwr7 | FileCheck %s
+target datalayout = "E-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-f128:128:128-v128:128:128-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+define void @foo(i32* %P) #0 {
+entry:
+  %tobool = icmp eq i32* %P, null
+  br i1 %tobool, label %if.end, label %if.then
+
+if.then:                                          ; preds = %entry
+  store i32 0, i32* %P, align 4, !tbaa !0
+  br label %if.end
+
+if.end:                                           ; preds = %entry, %if.then
+  ret void
+
+; CHECK: @foo
+; CHECK: beqlr
+; CHECK: blr
+}
+
+define void @bar(i32* %P, i32* %Q) #0 {
+entry:
+  %tobool = icmp eq i32* %P, null
+  br i1 %tobool, label %if.else, label %if.then
+
+if.then:                                          ; preds = %entry
+  store i32 0, i32* %P, align 4, !tbaa !0
+  %tobool1 = icmp eq i32* %Q, null
+  br i1 %tobool1, label %if.end3, label %if.then2
+
+if.then2:                                         ; preds = %if.then
+  store i32 1, i32* %Q, align 4, !tbaa !0
+  br label %if.end3
+
+if.else:                                          ; preds = %entry
+  store i32 0, i32* %Q, align 4, !tbaa !0
+  br label %if.end3
+
+if.end3:                                          ; preds = %if.then, %if.then2, %if.else
+  ret void
+
+; CHECK: @bar
+; CHECK: beqlr
+; CHECK: blr
+}
+
+attributes #0 = { nounwind }
+
+!0 = metadata !{metadata !"int", metadata !1}
+!1 = metadata !{metadata !"omnipotent char", metadata !2}
+!2 = metadata !{metadata !"Simple C/C++ TBAA"}

test/CodeGen/PowerPC/rounding-ops.ll

@@ -107,9 +107,10 @@ define double @test10(double %x) nounwind  {
 
 declare double @trunc(double) nounwind readnone
 
-define float @test11(float %x) nounwind  {
+define void @test11(float %x, float* %y) nounwind  {
   %call = tail call float @rintf(float %x) nounwind readnone
-  ret float %call
+  store float %call, float* %y
+  ret void
 
 ; CHECK: test11:
 ; CHECK-NOT: frin
@@ -125,9 +126,10 @@ define float @test11(float %x) nounwind  {
 
 declare float @rintf(float) nounwind readnone
 
-define double @test12(double %x) nounwind  {
+define void @test12(double %x, double* %y) nounwind  {
   %call = tail call double @rint(double %x) nounwind readnone
-  ret double %call
+  store double %call, double* %y
+  ret void
 
 ; CHECK: test12:
 ; CHECK-NOT: frin