From 439e2c92426c59f84d51bfb594e9ac86d496c708 Mon Sep 17 00:00:00 2001
From: gingerBill <bill@gingerbill.org>
Date: Mon, 29 Mar 2021 23:15:31 +0100
Subject: [PATCH] Fix shifting limits and LLVM code gen bug relating to shifts

---
 src/ir.cpp               | 13 +++++++------
 src/llvm_backend.cpp     | 14 ++++++++------
 src/llvm_backend_opt.cpp |  3 ++-
 3 files changed, 17 insertions(+), 13 deletions(-)

diff --git a/src/ir.cpp b/src/ir.cpp
index 96595c38d..090967ad8 100644
--- a/src/ir.cpp
+++ b/src/ir.cpp
@@ -4639,13 +4639,13 @@ handle_op:
 
 			irValue *bits = right;
 
-			irValue *max = ir_value_constant(type, exact_value_i64(8*type_size_of(type)));
-			irValue *less_equal_width = ir_emit(proc, ir_instr_binary_op(proc, Token_Lt, bits, max, t_llvm_bool));
+			irValue *bit_size = ir_value_constant(type, exact_value_i64(8*type_size_of(type)));
+			irValue *width_test = ir_emit(proc, ir_instr_binary_op(proc, Token_Lt, bits, bit_size, t_llvm_bool));
 
 
 			irValue *zero = ir_value_constant(type, exact_value_i64(0));
 			irValue *res = ir_emit(proc, ir_instr_binary_op(proc, op, left, bits, type));
-			return ir_emit_select(proc, less_equal_width, res, zero);
+			return ir_emit_select(proc, width_test, res, zero);
 		}
 	case Token_Shr:
 		{
@@ -4655,10 +4655,11 @@ handle_op:
 
 			irValue *bits = right;
 
-			irValue *max = ir_value_constant(type, exact_value_i64(8*type_size_of(type)));
-			irValue *less_equal_width = ir_emit(proc, ir_instr_binary_op(proc, Token_Lt, bits, max, t_llvm_bool));
+			irValue *bit_size = ir_value_constant(type, exact_value_i64(8*type_size_of(type)));
+			irValue *max = ir_value_constant(type, exact_value_i64(8*type_size_of(type)-1));
+			irValue *width_test = ir_emit(proc, ir_instr_binary_op(proc, Token_Lt, bits, bit_size, t_llvm_bool));
 
-			bits = ir_emit_select(proc, less_equal_width, bits, max);
+			bits = ir_emit_select(proc, width_test, bits, max);
 			return ir_emit(proc, ir_instr_binary_op(proc, op, left, bits, type));
 		}
 
diff --git a/src/llvm_backend.cpp b/src/llvm_backend.cpp
index 14a49b7da..92b180f73 100644
--- a/src/llvm_backend.cpp
+++ b/src/llvm_backend.cpp
@@ -6599,13 +6599,14 @@ handle_op:
 			LLVMValueRef lhsval = lhs.value;
 			LLVMValueRef bits = rhs.value;
 
-			LLVMValueRef max = LLVMConstInt(lb_type(p->module, rhs.type), 8*type_size_of(lhs.type), false);
+			LLVMValueRef bit_size = LLVMConstInt(lb_type(p->module, rhs.type), 8*type_size_of(lhs.type), false);
+			LLVMValueRef max = LLVMConstInt(lb_type(p->module, rhs.type), 8*type_size_of(lhs.type)-1, false);
 
-			LLVMValueRef less_equal_width = LLVMBuildICmp(p->builder, LLVMIntULT, bits, max, "");
+			LLVMValueRef width_test = LLVMBuildICmp(p->builder, LLVMIntULT, bits, bit_size, "");
 
 			res.value = LLVMBuildShl(p->builder, lhsval, bits, "");
 			LLVMValueRef zero = LLVMConstNull(lb_type(p->module, lhs.type));
-			res.value = LLVMBuildSelect(p->builder, less_equal_width, res.value, zero, "");
+			res.value = LLVMBuildSelect(p->builder, width_test, res.value, zero, "");
 			return res;
 		}
 	case Token_Shr:
@@ -6615,11 +6616,12 @@ handle_op:
 			LLVMValueRef bits = rhs.value;
 			bool is_unsigned = is_type_unsigned(type);
 
-			LLVMValueRef max = LLVMConstInt(lb_type(p->module, rhs.type), 8*type_size_of(lhs.type), false);
+			LLVMValueRef bit_size = LLVMConstInt(lb_type(p->module, rhs.type), 8*type_size_of(lhs.type), false);
+			LLVMValueRef max = LLVMConstInt(lb_type(p->module, rhs.type), 8*type_size_of(lhs.type)-1, false);
 
-			LLVMValueRef less_equal_width = LLVMBuildICmp(p->builder, LLVMIntULT, bits, max, "");
+			LLVMValueRef width_test = LLVMBuildICmp(p->builder, LLVMIntULT, bits, bit_size, "");
 
-			bits = LLVMBuildSelect(p->builder, less_equal_width, bits, max, "");
+			bits = LLVMBuildSelect(p->builder, width_test, bits, max, "");
 			if (is_unsigned) {
 				res.value = LLVMBuildLShr(p->builder, lhs.value, bits, "");
 			} else {
diff --git a/src/llvm_backend_opt.cpp b/src/llvm_backend_opt.cpp
index d8b1f8e75..cc2610ec5 100644
--- a/src/llvm_backend_opt.cpp
+++ b/src/llvm_backend_opt.cpp
@@ -8,8 +8,9 @@ void lb_populate_function_pass_manager(LLVMPassManagerRef fpm, bool ignore_memcp
 	}
 	LLVMAddPromoteMemoryToRegisterPass(fpm);
 	LLVMAddMergedLoadStoreMotionPass(fpm);
+	LLVMAddConstantPropagationPass(fpm);
 	LLVMAddEarlyCSEPass(fpm);
-	// LLVMAddEarlyCSEMemSSAPass(fpm);
+
 	LLVMAddConstantPropagationPass(fpm);
 	LLVMAddMergedLoadStoreMotionPass(fpm);
 	LLVMAddPromoteMemoryToRegisterPass(fpm);