[LLVMbugs] [Bug 16991] New: fast selector fails to select many blocks

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=16991

            Bug ID: 16991
           Summary: fast selector fails to select many blocks
           Product: libraries
           Version: trunk
          Hardware: PC
                OS: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: Backend: PowerPC
          Assignee: unassignedbugs at nondot.org
          Reporter: echristo at gmail.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified

>From the trivial C code:

void EmptyLoop() {
  for (long i = 0; i < 1000000000; ++i) {    
  }
}

We're missing in a few places:

ghostwheel:~> ~/builds/build-llvm/Debug+Asserts/bin/llc -fast-isel-verbose
empty_loop.ll -O0
FastISel miss:   store i64 0, i64* %i, align 8
FastISel miss:   br i1 %cmp, label %for.body, label %for.end
FastISel missed terminator:   ret void
FastISel miss:   store i64 %inc, i64* %i, align 8

and the full module:

; ModuleID = 'empty_loop.cpp'
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--linux-gnu"

; Function Attrs: nounwind
define void @_Z9EmptyLoopv() #0 {
entry:
  %i = alloca i64, align 8
  store i64 0, i64* %i, align 8
  br label %for.cond

for.cond:                                         ; preds = %for.inc, %entry
  %0 = load i64* %i, align 8
  %cmp = icmp slt i64 %0, 1000000000
  br i1 %cmp, label %for.body, label %for.end

for.body:                                         ; preds = %for.cond
  br label %for.inc

for.inc:                                          ; preds = %for.body
  %1 = load i64* %i, align 8
  %inc = add nsw i64 %1, 1
  store i64 %inc, i64* %i, align 8
  br label %for.cond

for.end:                                          ; preds = %for.cond
  ret void
}

attributes #0 = { nounwind "less-precise-fpmad"="false"
"no-frame-pointer-elim"="true" "no-frame-pointer-elim-non-leaf"
"no-infs-fp-math"="false" "no-nans-fp-math"="false"
"stack-protector-buffer-size"="8" "unsafe-fp-math"="false"
"use-soft-float"="false" }

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