[LLVMbugs] [Bug 11420] New: Dead store elimination eliminates live stores

[bugzilla-daemon at llvm.org]

http://llvm.org/bugs/show_bug.cgi?id=11420

             Bug #: 11420
           Summary: Dead store elimination eliminates live stores
           Product: new-bugs
           Version: trunk
          Platform: PC
        OS/Version: Linux
            Status: NEW
          Severity: normal
          Priority: P
         Component: new bugs
        AssignedTo: unassignedbugs at nondot.org
        ReportedBy: dschuff at google.com
                CC: llvmbugs at cs.uiuc.edu
    Classification: Unclassified


Created attachment 7637
  --> http://llvm.org/bugs/attachment.cgi?id=7637
LL file containing example code

This code is generated from the byval-alignment unittest.
struct s0 {
  long double x, y;
};
struct s0 g0;
void f0(int i, struct s0 y) {
  g0 = y;
  g0.x += i;
  g0.y += i;
}
Here is the IR before DSE:

dschuff at dschuff:/ulg/llvm-upstream/install$ cat ../llvm/dstest2.ll
target datalayout =
"e-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-p:32:32:32-v128:32:32"
%struct.s0 = type { double, double }
@g0 = common global %struct.s0 zeroinitializer, align 8

define internal fastcc void @f0(double %y.0, double %y.1) nounwind noinline {
entry:
  %y = alloca %struct.s0
  %.0 = getelementptr %struct.s0* %y, i32 0, i32 0
  store double %y.0, double* %.0  <------ initialize the temp struct
  %.1 = getelementptr %struct.s0* %y, i32 0, i32 1
  store double %y.1, double* %.1  <------ and the rest of it
  %0 = bitcast %struct.s0* %y to i8*
  tail call void @llvm.memcpy.p0i8.p0i8.i32(i8* bitcast (%struct.s0* @g0 to
i8*), i8* %0, i32 16, i32 8, i1 false) <----- now copy it to the global struct
  %1 = load double* getelementptr inbounds (%struct.s0* @g0, i32 0, i32 0),
align 8
  %add = fadd double %1, 1.000000e+00
  store double %add, double* getelementptr inbounds (%struct.s0* @g0, i32 0,
i32 0), align 8
  %2 = load double* getelementptr inbounds (%struct.s0* @g0, i32 0, i32 1),
align 8
  %add2 = fadd double %2, 1.000000e+00
  store double %add2, double* getelementptr inbounds (%struct.s0* @g0, i32 0,
i32 1), align 8
  ret void
}

declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture, i8* nocapture, i32, i32,
i1) nounwind

now run DSE:

bin/opt -basicaa -dse -S -o - ../llvm/dstest2.ll 
; ModuleID = '../llvm/dstest2.ll'
target datalayout =
"e-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-p:32:32:32-v128:32:32"

%struct.s0 = type { double, double }

@g0 = common global %struct.s0 zeroinitializer, align 8

define internal fastcc void @f0(double %y.0, double %y.1) nounwind noinline {
entry:
  %y = alloca %struct.s0
  %0 = bitcast %struct.s0* %y to i8*
  tail call void @llvm.memcpy.p0i8.p0i8.i32(i8* bitcast (%struct.s0* @g0 to
i8*), i8* %0, i32 16, i32 8, i1 false) <------ memcpy the UNINITIALIZED local
struct
  %1 = load double* getelementptr inbounds (%struct.s0* @g0, i32 0, i32 0),
align 8
  %add = fadd double %1, 1.000000e+00
  store double %add, double* getelementptr inbounds (%struct.s0* @g0, i32 0,
i32 0), align 8
  %2 = load double* getelementptr inbounds (%struct.s0* @g0, i32 0, i32 1),
align 8
  %add2 = fadd double %2, 1.000000e+00
  store double %add2, double* getelementptr inbounds (%struct.s0* @g0, i32 0,
i32 1), align 8
  ret void
}

declare void @llvm.memcpy.p0i8.p0i8.i32(i8* nocapture, i8* nocapture, i32, i32,
i1) nounwind

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