[llvm-bugs] [Bug 26391] New: Invalid defs/uses of the FPSW register after register allocation

[via llvm-bugs]

https://llvm.org/bugs/show_bug.cgi?id=26391

            Bug ID: 26391
           Summary: Invalid defs/uses of the FPSW register after register
                    allocation
           Product: new-bugs
           Version: trunk
          Hardware: PC
                OS: All
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
          Assignee: unassignedbugs at nondot.org
          Reporter: dimitry at andric.com
                CC: david.majnemer at gmail.com, jsweval at arxan.com,
                    kwm at FreeBSD.org, llvm-bugs at lists.llvm.org,
                    matze at braunis.de, qcolombet at apple.com
        Depends on: 21903
    Classification: Unclassified

+++ This bug was initially created as a clone of Bug #21903 +++

According to Matthias Braun, this test case is probably exposing a slightly
different problem with the internal representation.  Minimized C++ test case:

int x0, x1, x2;
double x3, x4;
int x5(double x6, double x7) {
  if (x4 && x6 < x7)
    x0 = 1;
  else
    x0 = 0;
  return x0;
}
void x8(double x6, double x7, bool &x9, double x10, double x11) {
  if (x2 == 0)
    x9 = 0;
  if (x2 == 1 && x5(x1, 0) && x5(x6, 0) && x5(x7, x11))
    x9 = 1;
  if (x2 == 6)
    x9 = 0;
  if (x2 == 7 && x5(x1, x3) && x5(x6, x10) && x5(x7, x11))
    x9 = 1;
}

Reproduce with: clang -cc1 -triple i386 -emit-obj -target-cpu i686 -O2 -w
testcase.cpp

Resulting in:

*** Bad machine code: MBB exits via conditional branch/fall-through but the CFG
successors don't match the actual successors! ***
- function:    _Z2x8ddRbdd
- basic block: BB#2 land.lhs.true (0x7fa392846b38)

*** Bad machine code: Using an undefined physical register ***
- function:    _Z2x8ddRbdd
- basic block: BB#5 land.lhs.true14 (0x7fa392846ea8)
- instruction: FNSTSW16r
- operand 1:   %FPSW<imp-use,kill>

*** Bad machine code: Using an undefined physical register ***
- function:    _Z2x8ddRbdd
- basic block: BB#11 land.lhs.true14 (0x7fa392846be8)
- instruction: %EAX<def> = MOVZX32rr8
- operand 1:   %AL<kill>

*** Bad machine code: Using an undefined physical register ***
- function:    _Z2x8ddRbdd
- basic block: BB#11 land.lhs.true14 (0x7fa392846be8)
- instruction: %EDX<def> = MOV32rm
- operand 1:   %EDX<kill>
fatal error: error in backend: Found 4 machine code errors.

Further reduced to .ll form by David Majnemer, to:

target datalayout = "e-m:e-p:32:32-f64:32:64-f80:32-n8:16:32-S128"
target triple = "i686--linux-gnu"

define void @f(double %p1, double %p2, double %p3, double %p4, i32 %p5, i8*
%p6, double %p7, double %p8, double %p9) align 2 {
entry:
  %cmp.i54 = fcmp olt double %p2, %p8
  %tobool.i45 = fcmp une double %p4, 0.000000e+00
  switch i32 %p5, label %if.end20 [
    i32 0, label %if.then10
    i32 1, label %land.lhs.true
    i32 2, label %if.then10
    i32 4, label %land.lhs.true13
  ]

land.lhs.true:                                    ; preds = %entry
  br i1 undef, label %land.lhs.true3, label %if.end20

land.lhs.true3:                                   ; preds = %land.lhs.true15,
%land.lhs.true
  br i1 %cmp.i54, label %land.lhs.true5, label %if.end20

land.lhs.true5:                                   ; preds = %land.lhs.true3
  %cmp.i50 = fcmp olt double %p3, %p9
  br i1 %cmp.i50, label %if.then10, label %if.end20

if.then10:                                        ; preds = %land.lhs.true5,
%entry, %entry
  store i8 1, i8* %p6, align 1
  br label %if.end20

land.lhs.true13:                                  ; preds = %entry
  %cmp.i46 = fcmp olt double %p1, %p7
  %or.cond.i47 = and i1 %tobool.i45, %cmp.i46
  %storemerge.i48 = zext i1 %or.cond.i47 to i32
  br i1 %or.cond.i47, label %land.lhs.true15, label %if.end20

land.lhs.true15:                                  ; preds = %land.lhs.true13
  %storemerge.i44 = zext i1 %cmp.i54 to i32
  br label %land.lhs.true3

if.end20:                                         ; preds = %land.lhs.true13,
%if.then10, %land.lhs.true5, %land.lhs.true3, %land.lhs.true, %entry
  ret void
}

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