[Thumb] Fix crash in Thumb1RegisterInfo::rewriteFrameIndex

[olista01]

Summary

This function can, for some offsets from the SP, split one instruction
into two. Since it re-uses the original instruction as the first
instruction of the result, we need ensure its result register is not
marked as dead before we use it in the second instruction.

[t.p.northover]

Hi Oliver,

This looks fine to me.

Tim.

[olista01]

Thanks, committed as r220194.

lib/Target/ARM/Thumb1RegisterInfo.cpp

if (Offset > 0) {
         removeOperands(MI, FrameRegIdx);
         AddDefaultPred(AddDefaultT1CC(MIB).addReg(FrameReg).addImm(Mask));
       } else {
         MI.getOperand(FrameRegIdx).ChangeToRegister(FrameReg, false);
         MI.getOperand(FrameRegIdx+1).ChangeToImmediate(Mask);
       }
       Offset = (Offset - Mask * Scale);
       MachineBasicBlock::iterator NII = std::next(II);
+      MI.getOperand(0).setIsDead(false);
       emitThumbRegPlusImmediate(MBB, NII, dl, DestReg, DestReg, Offset, TII,
                                 *this);
     } else {
       // Translate r0 = add sp, -imm to
       // r0 = -imm (this is then translated into a series of instructions)
       // r0 = add r0, sp
       emitThumbConstant(MBB, II, DestReg, Offset, TII, *this, dl);
 

test/CodeGen/Thumb/large-stack.ll

 ; CHECK: mov sp, r4
     %retval = alloca i32, align 4
     %tmp = alloca i32, align 4
     %a = alloca [805306369 x i8], align 16
     store i32 0, i32* %tmp
     %tmp1 = load i32* %tmp
     ret i32 %tmp1
 }
+
+; Here, the adds get optimized out because they are dead, but the calculation
+; of the address of stack_a is dead but not optimized out. When the address
+; calculation gets expanded to two instructions, we need to avoid reading a
+; dead register.
+; No CHECK lines (just test for crashes), as we hope this will be optimised
+; better in future.
+define i32 @test4() {
+entry:
+  %stack_a = alloca i8, align 1
+  %stack_b = alloca [256 x i32*], align 4
+  %int = ptrtoint i8* %stack_a to i32
+  %add = add i32 %int, 1
+  br label %block2
+
+block2:
+  %add2 = add i32 %add, 1
+  ret i32 0
+}