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Prevent redundant casts and create fewer LLVM builders #105549

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68 changes: 38 additions & 30 deletions compiler/rustc_codegen_llvm/src/builder.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -166,7 +166,7 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
}

fn switch_to_block(&mut self, llbb: Self::BasicBlock) {
*self = Self::build(self.cx, llbb)
unsafe { llvm::LLVMPositionBuilderAtEnd(self.llbuilder, llbb) }
}

fn ret_void(&mut self) {
Expand Down Expand Up @@ -412,10 +412,8 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
}

fn alloca(&mut self, ty: &'ll Type, align: Align) -> &'ll Value {
let mut bx = Builder::with_cx(self.cx);
bx.position_at_start(unsafe { llvm::LLVMGetFirstBasicBlock(self.llfn()) });
unsafe {
let alloca = llvm::LLVMBuildAlloca(bx.llbuilder, ty, UNNAMED);
let alloca = llvm::LLVMBuildAlloca(self.llbuilder, ty, UNNAMED);
llvm::LLVMSetAlignment(alloca, align.bytes() as c_uint);
alloca
}
Expand Down Expand Up @@ -566,33 +564,31 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
let start = dest.project_index(self, zero).llval;
let end = dest.project_index(self, count).llval;

let intro_bb = self.llbb();
let header_bb = self.append_sibling_block("repeat_loop_header");
let body_bb = self.append_sibling_block("repeat_loop_body");
let next_bb = self.append_sibling_block("repeat_loop_next");

self.br(header_bb);

let mut header_bx = Self::build(self.cx, header_bb);
let current = header_bx.phi(self.val_ty(start), &[start], &[self.llbb()]);
self.switch_to_block(header_bb);
let current = self.phi(self.val_ty(start), &[start], &[intro_bb]);

let keep_going = header_bx.icmp(IntPredicate::IntNE, current, end);
header_bx.cond_br(keep_going, body_bb, next_bb);
let keep_going = self.icmp(IntPredicate::IntNE, current, end);
self.cond_br(keep_going, body_bb, next_bb);

let mut body_bx = Self::build(self.cx, body_bb);
self.switch_to_block(body_bb);
let align = dest.align.restrict_for_offset(dest.layout.field(self.cx(), 0).size);
cg_elem
.val
.store(&mut body_bx, PlaceRef::new_sized_aligned(current, cg_elem.layout, align));

let next = body_bx.inbounds_gep(
self.backend_type(cg_elem.layout),
current,
&[self.const_usize(1)],
);
body_bx.br(header_bb);
header_bx.add_incoming_to_phi(current, next, body_bb);
cg_elem.val.store(self, PlaceRef::new_sized_aligned(current, cg_elem.layout, align));

let next =
self.inbounds_gep(self.backend_type(cg_elem.layout), current, &[self.const_usize(1)]);
self.br(header_bb);

*self = Self::build(self.cx, next_bb);
self.switch_to_block(header_bb);
self.add_incoming_to_phi(current, next, body_bb);

self.switch_to_block(next_bb);
}

fn range_metadata(&mut self, load: &'ll Value, range: WrappingRange) {
Expand Down Expand Up @@ -819,15 +815,33 @@ impl<'a, 'll, 'tcx> BuilderMethods<'a, 'tcx> for Builder<'a, 'll, 'tcx> {
}

fn bitcast(&mut self, val: &'ll Value, dest_ty: &'ll Type) -> &'ll Value {
unsafe { llvm::LLVMBuildBitCast(self.llbuilder, val, dest_ty, UNNAMED) }
unsafe {
if llvm::LLVMTypeOf(val) != dest_ty {
llvm::LLVMBuildBitCast(self.llbuilder, val, dest_ty, UNNAMED)
} else {
val
}
}
}

fn intcast(&mut self, val: &'ll Value, dest_ty: &'ll Type, is_signed: bool) -> &'ll Value {
unsafe { llvm::LLVMRustBuildIntCast(self.llbuilder, val, dest_ty, is_signed) }
unsafe {
if llvm::LLVMTypeOf(val) != dest_ty {
llvm::LLVMRustBuildIntCast(self.llbuilder, val, dest_ty, is_signed)
} else {
val
}
}
}

fn pointercast(&mut self, val: &'ll Value, dest_ty: &'ll Type) -> &'ll Value {
unsafe { llvm::LLVMBuildPointerCast(self.llbuilder, val, dest_ty, UNNAMED) }
unsafe {
if llvm::LLVMTypeOf(val) != dest_ty {
llvm::LLVMBuildPointerCast(self.llbuilder, val, dest_ty, UNNAMED)
} else {
val
}
Comment on lines +839 to +843
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@tmiasko tmiasko Dec 11, 2022

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Doesn't builder fold this at construction already https://github.com/rust-lang/llvm-project/blob/3dfd4d93fa013e1c0578d3ceac5c8f4ebba4b6ec/llvm/include/llvm/IR/IRBuilder.h#L1998-L2005?

}
}

/* Comparisons */
Expand Down Expand Up @@ -1206,12 +1220,6 @@ impl<'a, 'll, 'tcx> Builder<'a, 'll, 'tcx> {
unsafe { llvm::LLVMGetBasicBlockParent(self.llbb()) }
}

fn position_at_start(&mut self, llbb: &'ll BasicBlock) {
unsafe {
llvm::LLVMRustPositionBuilderAtStart(self.llbuilder, llbb);
}
}

fn align_metadata(&mut self, load: &'ll Value, align: Align) {
unsafe {
let v = [self.cx.const_u64(align.bytes())];
Expand Down