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[RISCV] Add support for call returns to RISCVSExtWRemoval.
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The implementation is inspired by code from PPCInstrInfo.

We look for a copy from X10(A0) preceded by an ADJCALLSTACKUP and
a PseudoCall. We use the PseudoCall to look up the IR function being
called to find it's return attributes.

Reviewed By: asb

Differential Revision: https://reviews.llvm.org/D139808
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@topperc
topperc committed Dec 13, 2022
1 parent ecabba0 commit 844430b
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Showing 2 changed files with 155 additions and 2 deletions.
37 changes: 35 additions & 2 deletions llvm/lib/Target/RISCV/RISCVSExtWRemoval.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -365,9 +365,42 @@ static bool isSignExtendedW(Register SrcReg, MachineRegisterInfo &MRI,
continue;
}

// TODO: Handle returns from calls?
Register CopySrcReg = MI->getOperand(1).getReg();
if (CopySrcReg == RISCV::X10) {
// For a method return value, we check the ZExt/SExt flags in attribute.
// We assume the following code sequence for method call.
// PseudoCALL @bar, ...
// ADJCALLSTACKUP 0, 0, implicit-def dead $x2, implicit $x2
// %0:gpr = COPY $x10
//
// We use the PseudoCall to look up the IR function being called to find
// its return attributes.
const MachineBasicBlock *MBB = MI->getParent();
auto II = MI->getIterator();
if (II == MBB->instr_begin() ||
(--II)->getOpcode() != RISCV::ADJCALLSTACKUP)
return false;

if (!AddRegDefToWorkList(MI->getOperand(1).getReg()))
const MachineInstr &CallMI = *(--II);
if (!CallMI.isCall() || !CallMI.getOperand(0).isGlobal())
return false;

auto *CalleeFn =
dyn_cast_if_present<Function>(CallMI.getOperand(0).getGlobal());
if (!CalleeFn)
return false;

auto *IntTy = dyn_cast<IntegerType>(CalleeFn->getReturnType());
if (!IntTy)
return false;

const AttributeSet &Attrs = CalleeFn->getAttributes().getRetAttrs();
unsigned BitWidth = IntTy->getBitWidth();
return (BitWidth <= 32 && Attrs.hasAttribute(Attribute::SExt)) ||
(BitWidth < 32 && Attrs.hasAttribute(Attribute::ZExt));
}

if (!AddRegDefToWorkList(CopySrcReg))
return false;

break;
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120 changes: 120 additions & 0 deletions llvm/test/CodeGen/RISCV/sextw-removal.ll
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Original file line number Diff line number Diff line change
Expand Up @@ -1146,3 +1146,123 @@ cleanup: ; preds = %entry, %if.end
%retval.0 = phi i32 [ %r.4, %if.end ], [ 0, %entry ]
ret i32 %retval.0
}

define void @test16(i32 signext %arg, i32 signext %arg1) nounwind {
; CHECK-LABEL: test16:
; CHECK: # %bb.0: # %bb
; CHECK-NEXT: addi sp, sp, -32
; CHECK-NEXT: sd ra, 24(sp) # 8-byte Folded Spill
; CHECK-NEXT: sd s0, 16(sp) # 8-byte Folded Spill
; CHECK-NEXT: sd s1, 8(sp) # 8-byte Folded Spill
; CHECK-NEXT: mv s0, a1
; CHECK-NEXT: call bar@plt
; CHECK-NEXT: mv s1, a0
; CHECK-NEXT: .LBB19_1: # %bb2
; CHECK-NEXT: # =>This Inner Loop Header: Depth=1
; CHECK-NEXT: mv a0, s1
; CHECK-NEXT: call bar@plt
; CHECK-NEXT: sllw s1, s1, s0
; CHECK-NEXT: bnez a0, .LBB19_1
; CHECK-NEXT: # %bb.2: # %bb7
; CHECK-NEXT: ld ra, 24(sp) # 8-byte Folded Reload
; CHECK-NEXT: ld s0, 16(sp) # 8-byte Folded Reload
; CHECK-NEXT: ld s1, 8(sp) # 8-byte Folded Reload
; CHECK-NEXT: addi sp, sp, 32
; CHECK-NEXT: ret
;
; NOREMOVAL-LABEL: test16:
; NOREMOVAL: # %bb.0: # %bb
; NOREMOVAL-NEXT: addi sp, sp, -32
; NOREMOVAL-NEXT: sd ra, 24(sp) # 8-byte Folded Spill
; NOREMOVAL-NEXT: sd s0, 16(sp) # 8-byte Folded Spill
; NOREMOVAL-NEXT: sd s1, 8(sp) # 8-byte Folded Spill
; NOREMOVAL-NEXT: mv s0, a1
; NOREMOVAL-NEXT: call bar@plt
; NOREMOVAL-NEXT: mv s1, a0
; NOREMOVAL-NEXT: .LBB19_1: # %bb2
; NOREMOVAL-NEXT: # =>This Inner Loop Header: Depth=1
; NOREMOVAL-NEXT: sext.w a0, s1
; NOREMOVAL-NEXT: call bar@plt
; NOREMOVAL-NEXT: sllw s1, s1, s0
; NOREMOVAL-NEXT: bnez a0, .LBB19_1
; NOREMOVAL-NEXT: # %bb.2: # %bb7
; NOREMOVAL-NEXT: ld ra, 24(sp) # 8-byte Folded Reload
; NOREMOVAL-NEXT: ld s0, 16(sp) # 8-byte Folded Reload
; NOREMOVAL-NEXT: ld s1, 8(sp) # 8-byte Folded Reload
; NOREMOVAL-NEXT: addi sp, sp, 32
; NOREMOVAL-NEXT: ret
bb:
%i = call signext i32 @bar(i32 signext %arg)
br label %bb2

bb2: ; preds = %bb2, %bb
%i3 = phi i32 [ %i, %bb ], [ %i5, %bb2 ]
%i4 = tail call signext i32 @bar(i32 signext %i3)
%i5 = shl i32 %i3, %arg1
%i6 = icmp eq i32 %i4, 0
br i1 %i6, label %bb7, label %bb2

bb7: ; preds = %bb2
ret void
}

define void @test17(i32 signext %arg, i32 signext %arg1) nounwind {
; CHECK-LABEL: test17:
; CHECK: # %bb.0: # %bb
; CHECK-NEXT: addi sp, sp, -32
; CHECK-NEXT: sd ra, 24(sp) # 8-byte Folded Spill
; CHECK-NEXT: sd s0, 16(sp) # 8-byte Folded Spill
; CHECK-NEXT: sd s1, 8(sp) # 8-byte Folded Spill
; CHECK-NEXT: mv s0, a1
; CHECK-NEXT: call bat@plt
; CHECK-NEXT: mv s1, a0
; CHECK-NEXT: .LBB20_1: # %bb2
; CHECK-NEXT: # =>This Inner Loop Header: Depth=1
; CHECK-NEXT: mv a0, s1
; CHECK-NEXT: call bar@plt
; CHECK-NEXT: sllw s1, s1, s0
; CHECK-NEXT: bnez a0, .LBB20_1
; CHECK-NEXT: # %bb.2: # %bb7
; CHECK-NEXT: ld ra, 24(sp) # 8-byte Folded Reload
; CHECK-NEXT: ld s0, 16(sp) # 8-byte Folded Reload
; CHECK-NEXT: ld s1, 8(sp) # 8-byte Folded Reload
; CHECK-NEXT: addi sp, sp, 32
; CHECK-NEXT: ret
;
; NOREMOVAL-LABEL: test17:
; NOREMOVAL: # %bb.0: # %bb
; NOREMOVAL-NEXT: addi sp, sp, -32
; NOREMOVAL-NEXT: sd ra, 24(sp) # 8-byte Folded Spill
; NOREMOVAL-NEXT: sd s0, 16(sp) # 8-byte Folded Spill
; NOREMOVAL-NEXT: sd s1, 8(sp) # 8-byte Folded Spill
; NOREMOVAL-NEXT: mv s0, a1
; NOREMOVAL-NEXT: call bat@plt
; NOREMOVAL-NEXT: mv s1, a0
; NOREMOVAL-NEXT: .LBB20_1: # %bb2
; NOREMOVAL-NEXT: # =>This Inner Loop Header: Depth=1
; NOREMOVAL-NEXT: sext.w a0, s1
; NOREMOVAL-NEXT: call bar@plt
; NOREMOVAL-NEXT: sllw s1, s1, s0
; NOREMOVAL-NEXT: bnez a0, .LBB20_1
; NOREMOVAL-NEXT: # %bb.2: # %bb7
; NOREMOVAL-NEXT: ld ra, 24(sp) # 8-byte Folded Reload
; NOREMOVAL-NEXT: ld s0, 16(sp) # 8-byte Folded Reload
; NOREMOVAL-NEXT: ld s1, 8(sp) # 8-byte Folded Reload
; NOREMOVAL-NEXT: addi sp, sp, 32
; NOREMOVAL-NEXT: ret
bb:
%i = call zeroext i16 @bat(i32 signext %arg)
%zext = zext i16 %i to i32
br label %bb2

bb2: ; preds = %bb2, %bb
%i3 = phi i32 [ %zext, %bb ], [ %i5, %bb2 ]
%i4 = tail call signext i32 @bar(i32 signext %i3)
%i5 = shl i32 %i3, %arg1
%i6 = icmp eq i32 %i4, 0
br i1 %i6, label %bb7, label %bb2

bb7: ; preds = %bb2
ret void
}
declare zeroext i16 @bat(i32 signext)

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