authorgravatar for timonkruiper@gmail.comTimon Kruiper <timonkruiper@gmail.com> 2021-01-05 18:35:42+01:00
committergravatar for timonkruiper@gmail.comTimon Kruiper <timonkruiper@gmail.com> 2021-01-06 10:52:20+01:00
log5d5db833f277518bab152b743d6a4cfaa1e3fd8d
treec7f898a8b063ccb8cf6c249a508ebec14dad0164
parent1149cd593e82b338058037c29bcd0e2caaab0dcb

stage2: hoist alloca instructions to top of function in LLVM backend

This way the generated code only has to setup the stack size at the beginning of a function and this improves codegen. Fixes #7689 ``` fn foo() void {} export fn hello(z: i8) void { var x: i16 = undefined; foo(); var y: i32 = 1; y += z; } ``` llvm-ir: ``` define void @hello(i8 %0) { Entry: %1 = alloca i8, align 1 %2 = alloca i16, align 2 %3 = alloca i32, align 4 store i8 %0, i8* %1, align 1 %4 = load i8, i8* %1, align 1 store i16 undef, i16* %2, align 2 call void @foo() store i32 1, i32* %3, align 4 %5 = load i32, i32* %3, align 4 %6 = sext i8 %4 to i32 %7 = add nsw i32 %5, %6 store i32 %7, i32* %3, align 4 ret void } ```

2 files changed, 44 insertions(+), 4 deletions(-)

src/llvm_backend.zig+35-4
...@@ -148,6 +148,9 @@ pub const LLVMIRModule = struct {...@@ -148,6 +148,9 @@ pub const LLVMIRModule = struct {
148 gpa: *Allocator,148 gpa: *Allocator,
149 err_msg: ?*Compilation.ErrorMsg = null,149 err_msg: ?*Compilation.ErrorMsg = null,
150150
151 // TODO: The fields below should really move into a different struct,
152 // because they are only valid when generating a function
153
151 /// This stores the LLVM values used in a function, such that they can be154 /// This stores the LLVM values used in a function, such that they can be
152 /// referred to in other instructions. This table is cleared before every function is generated.155 /// referred to in other instructions. This table is cleared before every function is generated.
153 func_inst_table: std.AutoHashMapUnmanaged(*Inst, *const llvm.Value) = .{},156 func_inst_table: std.AutoHashMapUnmanaged(*Inst, *const llvm.Value) = .{},
...@@ -156,6 +159,11 @@ pub const LLVMIRModule = struct {...@@ -156,6 +159,11 @@ pub const LLVMIRModule = struct {
156 args: []*const llvm.Value = &[_]*const llvm.Value{},159 args: []*const llvm.Value = &[_]*const llvm.Value{},
157 arg_index: usize = 0,160 arg_index: usize = 0,
158161
162 entry_block: *const llvm.BasicBlock = undefined,
163 /// This fields stores the last alloca instruction, such that we can append more alloca instructions
164 /// to the top of the function.
165 latest_alloca_inst: ?*const llvm.Value = null,
166
159 pub fn create(allocator: *Allocator, sub_path: []const u8, options: link.Options) !*LLVMIRModule {167 pub fn create(allocator: *Allocator, sub_path: []const u8, options: link.Options) !*LLVMIRModule {
160 const self = try allocator.create(LLVMIRModule);168 const self = try allocator.create(LLVMIRModule);
161 errdefer allocator.destroy(self);169 errdefer allocator.destroy(self);
...@@ -332,8 +340,9 @@ pub const LLVMIRModule = struct {...@@ -332,8 +340,9 @@ pub const LLVMIRModule = struct {
332 bb.deleteBasicBlock();340 bb.deleteBasicBlock();
333 }341 }
334342
335 const entry_block = llvm_func.appendBasicBlock("Entry");343 self.entry_block = llvm_func.appendBasicBlock("Entry");
336 self.builder.positionBuilderAtEnd(entry_block);344 self.builder.positionBuilderAtEnd(self.entry_block);
345 self.latest_alloca_inst = null;
337346
338 const instructions = func.body.instructions;347 const instructions = func.body.instructions;
339 for (instructions) |inst| {348 for (instructions) |inst| {
...@@ -476,7 +485,7 @@ pub const LLVMIRModule = struct {...@@ -476,7 +485,7 @@ pub const LLVMIRModule = struct {
476 const arg_val = self.args[self.arg_index];485 const arg_val = self.args[self.arg_index];
477 self.arg_index += 1;486 self.arg_index += 1;
478487
479 const ptr_val = self.builder.buildAlloca(try self.getLLVMType(inst.base.ty, inst.base.src), "");488 const ptr_val = self.buildAlloca(try self.getLLVMType(inst.base.ty, inst.base.src));
480 _ = self.builder.buildStore(arg_val, ptr_val);489 _ = self.builder.buildStore(arg_val, ptr_val);
481 return self.builder.buildLoad(ptr_val, "");490 return self.builder.buildLoad(ptr_val, "");
482 }491 }
...@@ -488,7 +497,29 @@ pub const LLVMIRModule = struct {...@@ -488,7 +497,29 @@ pub const LLVMIRModule = struct {
488497
489 // TODO: figure out a way to get the name of the var decl.498 // TODO: figure out a way to get the name of the var decl.
490 // TODO: set alignment and volatile499 // TODO: set alignment and volatile
491 return self.builder.buildAlloca(try self.getLLVMType(pointee_type, inst.base.src), "");500 return self.buildAlloca(try self.getLLVMType(pointee_type, inst.base.src));
501 }
502
503 /// Use this instead of builder.buildAlloca, because this function makes sure to
504 /// put the alloca instruction at the top of the function!
505 fn buildAlloca(self: *LLVMIRModule, t: *const llvm.Type) *const llvm.Value {
506 if (self.latest_alloca_inst) |latest_alloc| {
507 // builder.positionBuilder adds it before the instruction,
508 // but we want to put it after the last alloca instruction.
509 self.builder.positionBuilder(self.entry_block, latest_alloc.getNextInstruction().?);
510 } else {
511 // There might have been other instructions emitted before the
512 // first alloca has been generated. However the alloca should still
513 // be first in the function.
514 if (self.entry_block.getFirstInstruction()) |first_inst| {
515 self.builder.positionBuilder(self.entry_block, first_inst);
516 }
517 }
518 defer self.builder.positionBuilderAtEnd(self.entry_block);
519
520 const val = self.builder.buildAlloca(t, "");
521 self.latest_alloca_inst = val;
522 return val;
492 }523 }
493524
494 fn genStore(self: *LLVMIRModule, inst: *Inst.BinOp) !?*const llvm.Value {525 fn genStore(self: *LLVMIRModule, inst: *Inst.BinOp) !?*const llvm.Value {
src/llvm_bindings.zig+9
...@@ -17,6 +17,9 @@ pub const Value = opaque {...@@ -17,6 +17,9 @@ pub const Value = opaque {
17 pub const getFirstBasicBlock = LLVMGetFirstBasicBlock;17 pub const getFirstBasicBlock = LLVMGetFirstBasicBlock;
18 extern fn LLVMGetFirstBasicBlock(Fn: *const Value) ?*const BasicBlock;18 extern fn LLVMGetFirstBasicBlock(Fn: *const Value) ?*const BasicBlock;
1919
20 pub const getNextInstruction = LLVMGetNextInstruction;
21 extern fn LLVMGetNextInstruction(Inst: *const Value) ?*const Value;
22
20 // Helper functions23 // Helper functions
21 // TODO: Do we want to put these functions here? It allows for convienient function calls24 // TODO: Do we want to put these functions here? It allows for convienient function calls
22 // on Value: llvm_fn.addFnAttr("noreturn")25 // on Value: llvm_fn.addFnAttr("noreturn")
...@@ -138,6 +141,9 @@ pub const Builder = opaque {...@@ -138,6 +141,9 @@ pub const Builder = opaque {
138 pub const disposeBuilder = LLVMDisposeBuilder;141 pub const disposeBuilder = LLVMDisposeBuilder;
139 extern fn LLVMDisposeBuilder(Builder: *const Builder) void;142 extern fn LLVMDisposeBuilder(Builder: *const Builder) void;
140143
144 pub const positionBuilder = LLVMPositionBuilder;
145 extern fn LLVMPositionBuilder(Builder: *const Builder, Block: *const BasicBlock, Instr: *const Value) void;
146
141 pub const positionBuilderAtEnd = LLVMPositionBuilderAtEnd;147 pub const positionBuilderAtEnd = LLVMPositionBuilderAtEnd;
142 extern fn LLVMPositionBuilderAtEnd(Builder: *const Builder, Block: *const BasicBlock) void;148 extern fn LLVMPositionBuilderAtEnd(Builder: *const Builder, Block: *const BasicBlock) void;
143149
...@@ -196,6 +202,9 @@ pub const Builder = opaque {...@@ -196,6 +202,9 @@ pub const Builder = opaque {
196pub const BasicBlock = opaque {202pub const BasicBlock = opaque {
197 pub const deleteBasicBlock = LLVMDeleteBasicBlock;203 pub const deleteBasicBlock = LLVMDeleteBasicBlock;
198 extern fn LLVMDeleteBasicBlock(BB: *const BasicBlock) void;204 extern fn LLVMDeleteBasicBlock(BB: *const BasicBlock) void;
205
206 pub const getFirstInstruction = LLVMGetFirstInstruction;
207 extern fn LLVMGetFirstInstruction(BB: *const BasicBlock) ?*const Value;
199};208};
200209
201pub const TargetMachine = opaque {210pub const TargetMachine = opaque {